TBI 350 Target Idle Speed

[maronielb]

Hi guys, im in desperate need of help with my 93 silverado that has a 5.7L TBI motor, I have a high idle issue ive been chasing for a couple weeks now. I have done a full rebuild on the TB along with new injectors, new intake to TB gasket, New coolant temp sensor (scanner verified that its reading correctly) New idle air control value (yes i went through the calibration process) Adjusted TPS sensor to .59V. timing is set at 0 and there are no vacuum leaks but the truck still idles at 1k. So i decided to purchase an OBD1 scanner that shows live data i hooked up the scanner and i can see that the idle req is set at 1000 rpm so im starting to think that my computer is demanding a 1000 rpm idle and no mater what i do once its fully warmed up it idles at 1000 rpm in neutral (i have a 5 speed). So with all that being said i did research and found the BIN and XDF files for my truck and downloaded them and im able to view everything in tunerpro RT. My question to you guys is what perimeters does the computer use to determine idle speed? is it possible for the idle command to be set at 1k in the reman computer? my BCC code is AZDR which is the correct one for my truck and i opened up my computer to verify that is has the correct chip and it does. the previous owner had the computer changed with a reman one but i dont think that matters as the chip inside is still an AZDR. when i view the target idle rpm vs coolant temp in tunerpro for the AZDR bin and $9A XDF file i downloaded i see that when the coolant temp is 195 my idle should be between 650-700 but its not so thats why i want to know what perimeters are used to determine idle speed because obviously its not just the coolant temp.

[MO LS Noobie]

Throttle is open (.73V). Throttle 53%. What is the IAC value?

[TriumphR3]

Throttle is open (.73V). Throttle 53%. What is the IAC value?

Suggests the manual throttle setting may not be set right. Maronielb have you done the manual throttle set procedure?

[maronielb]

That picture was taken before i adjusted the TPS to .59V IAC counts fluctuate between 5-10

[maronielb]

What is the manual throttle set procedure? is that the one where you remove the cap and adjust the idle screw on the TB? if so no i havent and im not willing to mess with that, its set from the factory and is not suppose to be messed with.

[TriumphR3]

What is the manual throttle set procedure? is that the one where you remove the cap and adjust the idle screw on the TB? if so no i havent and im not willing to mess with that, its set from the factory and is not suppose to be messed with.

Ok, with all due respect, I beg to differ with you. 99% of the mechs that deal with TBI understand that at some point you have to set/adjust the manual setting. Especially if it has been rebuilt. Anyway, here is the procedure. Oh and what did your IAC value read?

https://www.gmcmi.com/wp-content/uploads/2013/02/TBI-Initial-calibration.pdf

[MO LS Noobie]

That picture was taken before i adjusted the TPS to .59V IAC counts fluctuate between 5-10

If your TPS and IAC are as stated, could be vacuum leak, especially check brake booster.

Desired idle is 650, that is what it is shooting for. You are getting more air somewhere. What are your block learn and integrator fuel trims?

[MO LS Noobie]

https://www.gmcmi.com/wp-content/uploads/2013/02/TBI-Initial-calibration.pdf[/QUOTE]

This is good info.

[steveo]

after making sure there are no leaks and timing is correct....any tbi i usually adjust the throttle plates so the IAC counts are in like 10-20 counts at full operating temp in neutral
its always worked for me
tbi is the only system where hot idle air should be all through the plates

[maronielb]

how would i check the brake booster? and yes i agree 650 sounds like the perfect idle speed. i have no idea what a block learn it or integrator fuel trims. i dont think my scanner shows those. i will post a poc tommorow with everything that my scanner shows.

[maronielb]

if all else fails i might just end up adjusting it manually even though i really dont want to.

[MO LS Noobie]

Pinch off hose going to Booster, this works for any regular, soft, rubber hose. There should be no change in idle speed, or fuel trims. Also test any vacuum lines to carbon canister, HVAC system, or anything else vacuum operated.

Block learn/integrator are the terms GM used for fuel trims, long/short term before OBD2. 128 equals 100%, or 0 trim. Below 128 is taking away fuel, above is adding fuel. Anything within 10% is considered normal.

[maronielb]

Ok i will try that tommorow, here are the pics from
All the data my scanner shows me, it does not so block learn or anything. Also i had adjusted myTPS to .59 but now it’s showing .65, does that mean the sensor is bad? Truck started idling at like 1300-1400 rpm today fully warmed up, I’m about to turn this thing to the ground

1977319772

[MO LS Noobie]

The thing that really stands out to me is the IAC is at 0%. First thing I would do is block off the air supply to the IAC, this is the kidney shaped hole next to the throttle blade directly above the IAC valve. Is there any air at all going through that valve? With 0% I there should not be any air at all. If there is air going through that valve then either the valve is bad, wiring, PCM, or the computer just hasn't learned the home position. See post number 6 by TriumphR3 above.

If there is NOT any air going through the IAC valve then you have too much air getting in some place, the most common place is the mounting gasket for the TBI unit, but you already replaced that. I use propane to sniff out vacuum leaks on the engine itself, typically a missing vacuum cap, compromised vacuum line, the PCV valve, or intake manifold leaks at the gasket. You can use carburetor cleaner to do the same thing, but it tends to puddle and is a severe fire hazard. Not being able to see the fuel trims makes things harder but you should be able to hear a vacuum leak because the engine will smooth out and speed up.

Do you have access to another scanner? There are a couple of other things that your scanner is showing but that IAC percentage is the first place I would look.

[maronielb]

So today i re did the IAC reset produce and reset the tps voltage to .59 again which brought my idle back down to about 1k. Then I checked all vacuum lines and pinched the line from the brake booster, and pcv valve and there was no change in idle. The IAC counts are now around 4-10. The thing is the scanner is showing a 1k idle requirement so no matter what i do the computer will still idle the truck at 1k. The whole reason for my original post was to find out how the computer determines the idle requirement so i could dig into that rather then just trying to chase my tail on this high idle

[tayto]

throttle shafts probably need bushings

[MO LS Noobie]

Base idle speed, coolant temp, AC, transmission gear, and engine cranking idle air all factor into the "idle required" rpm

[ralmo94]

Just throwing this out there as I did not notice it mentioned before, but is the coolant temp on the scanner reading correctly? As you probably know the dash gauge has a separate sender than the ECU. Does it flood easy when starting it?

[stew86MCSS396]

The thing that really stands out to me is the IAC is at 0%. First thing I would do is block off the air supply to the IAC, this is the kidney shaped hole next to the throttle blade directly above the IAC valve. Is there any air at all going through that valve? With 0% I there should not be any air at all. If there is air going through that valve then either the valve is bad, wiring, PCM, or the computer just hasn't learned the home position. See post number 6 by TriumphR3 above.

If there is NOT any air going through the IAC valve then you have too much air getting in some place, the most common place is the mounting gasket for the TBI unit, but you already replaced that. I use propane to sniff out vacuum leaks on the engine itself, typically a missing vacuum cap, compromised vacuum line, the PCV valve, or intake manifold leaks at the gasket. You can use carburetor cleaner to do the same thing, but it tends to puddle and is a severe fire hazard. Not being able to see the fuel trims makes things harder but you should be able to hear a vacuum leak because the engine will smooth out and speed up.

Do you have access to another scanner? There are a couple of other things that your scanner is showing but that IAC percentage is the first place I would look.
There was another forum post with a similar issue and the fix turned out to be the IAC was wired wrong. Idk how that mysteriously happens if no one messed with the wires...

Battery volts could be a little concerning. Not 100% if TBI has injector offsets vs batt volts and how that would affect idle quality??? That 53% throttle looks unusual too.

[Sledhead2]

I am late to the game, was truck running fine and then just started idling high?

Did you do any work to it and then it started?

Guys here is a left field question, if he cooked his O2 sensor, could/would it cause high idle?

[TriumphR3]

A faulty temp sensor that goes to the ecm can play havoc on idle rpm’s.

[maronielb]

Yes it is coolant reads at 195 on the scanner and it’s a brand new ac delco sensor

[ralmo94]

A faulty temp sensor that goes to the ecm can play havoc on idle rpm’s.
X2.
That's what I was wondering about because requested idle rpm high.

[ralmo94]

Yes it is coolant reads at 195 on the scanner and it’s a brand new ac delco sensor

Interesting

[maronielb]

Trucks always idle around 1k when i first bought it but i didn’t care because inwas going to rebuild the throttle body so i ended up rebuilding it about a year later and it stills idle the same

[maronielb]

Yeah I’m lost this thing has be pulling my hair

[maronielb]

It’s brand new ac Delco sensor and my scanner shows the computer is reading 195 degrees

[maronielb]

I havent messed with the wiring it’s still the factory plug

[maronielb]

Please elaborate on this, where can i get the bushings and it is hard to replace? How can i determine if i even need bushings!

[ralmo94]

I have messed with the wiring it’s still the factory plug
Off the top of my head, idle speed is determined by AC off or on, and Park Neutral, or in gear.Other than that it's temp. Does the air work, and does it have an auto?

[ralmo94]

Please elaborate on this, where can i get the bushings and it is hard to replace? How can i determine if i even need bushings!

If the ECU is requesting 1k idle rpm, it's not a vacuum leak.

[maronielb]

Don’t think base idle has ever been messed with because the plug is still there,
Coolant temp is reading correctly based on the scanner. Ac is off, transmission is a manual for that won’t affect it, and what’s cranking idle air? Is it possible that the base idle needs to be reset? I don’t see how it would get out of adjustment unless someone messed with the screw?

[ralmo94]

Do you have any trouble codes?

[maronielb]

Ac doesn’t work and it’s a manual trans

[maronielb]

None

[ralmo94]

Don’t think base idle has ever been messed with because the plug is still there,
Coolant temp is reading correctly based on the scanner. Ac is off, transmission is a manual for that won’t affect it, and what’s cranking idle air? Is it possible that the base idle needs to be reset? I don’t see how it would get out of adjustment unless someone messed with the screw?

If it was base adjustment the requested idle would be low and it wouldn't be able to get it that low. I don't know the BCC codes off the top of my head, is that a manual calibration, or a swapped truck?

[maronielb]

Exactly what I’m thinking!

[maronielb]

What should the throttle percentage be at idle? And i just put a brand new battery in it the other day so battery voltage shouldn’t be and issue anymore but when i took those pics it did have a weak battery

[maronielb]

Factory 5.7l manual bcc code is AZDR i opened the computer to make sure it has the correct chip in it and it does

[ralmo94]

If I remember correctly when data logging my 94, TPS read 0% at idle. Are you able to look at the idle flag? Should read true or false. Maybe your TPS is out of adjustment?

[maronielb]

My scanner does not show idle flag, and how would
I get the throttle to read 0% at idle? The tps is currently adjusted to .59v at idle with a 53% throttle

[ralmo94]

My scanner does not show idle flag, and how would
I get the throttle to read 0% at idle? The tps is currently adjusted to .59v at idle with a 53% throttle

53% throttle at idle? Did I read that correctly?

I would unplug the TPS while idling and see if it drops rpm, could also look at scanner and see if requested rpm goes down. There is no possible way it should be seeing 53% at idle. If it was 3% I would think maybe it's saying base idle is set at 3%, but 53% is halfway to the floor. Have you checked for a smooth voltage sweep on the TPS?

[maronielb]

TPS seems to have a smooth voltage sweep but I’ll try unplugging it and seeing what happens, the thing that confuses me the no matter what i do the idle requirement shows 1000 on the scanner and my truck idles at exactly 1000

[ralmo94]

Kinda has me stumped a little too. Does vehicle speed show correct in scanner also?
If you eliminate enough stuff you should eventually find it, sometimes it's hard to know where to go next though lol.

[maronielb]

I haven’t drivin it with the scanner hooked up to check vehicle speed, but yeah it’s driving me
Crazy, I’m gonna put a new tps sensor on it and see what happens

[MO LS Noobie]

Might try a different scanner, to see if it is lying to you. The other thing that could be causing a desired idle of 1000 would be what they call the throttle cracker, and throttle follower that basically act as the old dash pot that slowed the transition idle. Was this a manual transmission been to start with or is it converted from a automatic transmission? The automatic transmission bin has several rolling idle settings that affect idle while the vehicle is in motion.

Did you ever try plugging the hole for the IAC that I suggested much earlier?

[maronielb]

I don’t have access to another scanner and i just bought this one brand new for almost 200$, so i don’t want to buy another one and this Is a factory manual and I’ve confirmed the computer has the correct chip in it. I have not tried plugging the IAC hole, but i don’t see how this would set a desired idle of 1k anyway? If i remove the IAC and plug the hole then the truck should idle at what the base idle was set to at the factory. I’m starting to think it’s tps related since the tps numbers are the only ones that seem to be out of wack on the scanner

[ralmo94]

That's why I suggested unplugging the TPS, to see if it wants to command a lower idle speed with TPs disconnected. If it doesn't, I doubt a new TPS will do any good

[MO LS Noobie]

To be clear, you don't need to remove the IAC, just plug the hole from the top of the throttlebody.

[ralmo94]

To be clear, you don't need to remove the IAC, just plug the hole from the top of the throttlebody.

With all due respect, as the op was trying to point out, a hanging or malfunction iac wouldn't cause the ECU to command 1k idle rpm, if you cut off iac circuit air, you are still going to be the same requested idle speed, it just won't be able to attain it, unless I am missing something.

[MO LS Noobie]

With all due respect, as the op was trying to point out, a hanging or malfunction iac wouldn't cause the ECU to command 1k idle rpm, if you cut off iac circuit air, you are still going to be the same requested idle speed, it just won't be able to attain it, unless I am missing something.

Agreed, he has been chasing this issue for a while.

[maronielb]

I will do this tommorow and get back to you, last time i unplugged it the idle went higher

[maronielb]

Yes i have and I’m about to burn this truck if i don’t figure it out, i just spent 20k restoring this truck from the frame up and i can’t figure out a damn idle issue

[ralmo94]

I don’t have access to another scanner and i just bought this one brand new for almost 200$, so i don’t want to buy another one

Too bad you could have gotten a decent USB to aldl cable for about half that much, then you could pull the bin file from the diagnostic port and verify nobody has screwed with anything on it. Plus you could get a data log recording instead of just looking at a small scanner screen.

[maronielb]

When can i get the cable for $100? Last i checked it’s like $140 for. I’m still willing to purchase one if it’s $100

[ralmo94]

Boosted NW has them for $120, shows only one left in stock, RedDevilRiver if I'm reading correctly, is $55. If you had a serial port laptop you could make one, I've never done it before. There are a few on eBay for not a lot of $. Not sure who makes them

[ralmo94]

Also there is ALDLcables.com

[maronielb]

Would i use this cable with tuner pro? Also can you send me a link to the cable you have/would buy if you were in the market?

[ralmo94]

Would i use this cable with tuner pro? Also can you send me a link to the cable you have/would buy if you were in the market?

Yes you could use it with tunerpro rt, or aldl droid, or any other scanner or datalogger program for GM obd1. Tuner pro is probably going to have the most public support as most everyone on this site uses it. You'll need an adx file for your mask.

The one I have I got from moates, they are no longer in business, boosted NW has taken over their market to offer the same exact products moates used to offer, I like the idea of supporting such an effort. On the other hand the red devil river one comes with a disc, and it would be interesting to see what's on the disc.

[ralmo94]

Here is a link to $9a adx on this site. http://www.gearhead-efi.com/Fuel-Injection/showthread.php?1370-OBD1-Scanning-Datalogging-94-TBI-5-speed-manual&p=17006&viewfull=1#post17006

[ralmo94]

https://boostednw.com/emulation-cables/boostednw-aldl-12-pin-gm-datalogger

Boosted NW

http://aldlcables.com/

Aldl cables .com

https://reddevilriver.com/home-page/ols/products/gm-12-pin-aldl-to-usb-cable (https://reddevilriver.com/home-page/ols/products/gm-12-pin-aldl-to-usb-



cable)


Red devil river


https://reddevilriver.com/home-page/ols/products/gm-12-pin-aldl-scan-bluetooth

Bluetooth option

[maronielb]

Red devil river seems to be the cheapest one so i will
Probably go with that one. I just messaged them to see what the cd/usb are for. I’ll keep you updated. Also thank you for the ADX file, from my understanding that’s the one needed if i want to log data? At this point i don’t want to/need to log data do i? I just want to be able to see all live data the computer is receiving from the sensors and also it would be nice to view the parameters in my current chip. Will i be able to do that using tuner pro and getting that cable?

[ralmo94]

Seeing the live data is the same as datalogging. You just have the option to record it and play it back. Data logging is what you want to do.

To read the bin from aldl, you need @steavo's flashhack and yes you can use the cable for it. He wrote it to flash Fbody obd1.5, but you can pull the bin through aldl on any aldl ECU.
https://ecmhack.com/flashhack/

[maronielb]

Oh ok i see. Once i get the cable I’ll let you know if i have any questions, it seems like a complicated process to be able to view the parameters on my current chip so i might just data log to see what all the sensors are reading, although my current scanner pretty much shows me the data for my my sensors. What benefit would i have from using tuner pro to
Date log?

[ralmo94]

You will be able to record a data log and post the log file here, it should give you more info than your scanner, idle flag for one. Would be nice to verify that chip is stock, although far fetched, there is the possibility that someone has used a UV eraser and burnt something on the chip, used to be the old school way. But it is still concerning that it is showing 50% throttle at idle. Maybe it won't with the cable, i don't know. Did you get a chance to unplug the TPS yet?

[maronielb]

Not yet the truck is not stored at my house so i don’t see it everyday but i will tomorrow and update you

[maronielb]

Ok so yesterday i unplugged the tps sensor and the idle went up for a second and then went back down to where it was idling before i unplugged it. However something wierd happened yesterday when i was driving it i floored it and it made a grinding sound from what seemed to be the transmission and then the check Engine light came
On for a code 43? Can this be related possibly?

[ralmo94]

Did you have the scanner plugged in while TPs was unhooked? What was the requested idle speed, and TPS %

Code 43 knock sensor open or shorted, I wouldn't think so but I wouldn't try to say for sure. How's your firewall wiring near the exhaust manifold collector?

[maronielb]

Yes it was plugged in but not on data mode so it wouldn’t mess with the idle. After i
Unplugged the tps i then went into data mode to see the love data and the idle
Req was still at 1k and the tps voltage was 0 However the throttle percentage was showing 31%?are you talking about the wiring that runs through the metal shield thing that’s bolted to the transmission? I haven’t got
Underneath to look at it but the knock sensor
Plug was broken/brittle when i replaced the knock sensor so
I’m wondering if it fell off when i floored it.

[ralmo94]

I'm wondering if the 31% is a glitch in the scanner? Does it change when you apply throttle?

The plug could have gotten unplugged. My truck had an exhaust leak at the collector when I bought it and it melted a bunch of wires together, just wanted to make sure you didn't have that going on, since it read 0vlts when TPs unplugged, I don't think you do, but a visual inspection never hurts. Does it raise the idle if you jumper A and B of the aldl while it's running?

[maronielb]

Well i was thinking maybe the base idle is set to keep the Throttle at 31% open? I’ll check next time I’m with the truck, i couldn’t apply throttle with the tps unplugged the motor would choke, wires are all good i had the whole harness out of the truck a couple months ago and everything looked good expect brittle/half broken connection for the knock sensor. I’ll jump A and B and see if the idle increases. I’ve had the idle issue since the bought the truck and now that i rebuilt the throttle body and changed all these sensors i was hoping it would fix it but nope. Still wants to idle at 1k

[ralmo94]

31% is too much. Should be 0 with 0vlts I'm still thinking maybe it's a glitch with your scanner. I guess we'll find out after you get your Cable.

Could always do a 7427 swap. Lol

[MO LS Noobie]

See #46 above. When I see data that does not make sense I usually grab a different scanner. Sometimes the data just gets screwed up. I to await your results with the new cable, I think you will find a lot more than the 10 data list parameters that your current scanner gives you.

[maronielb]

What’s a 7427 swap?

[maronielb]

I’m still waiting for a response from red devil before i purchase the cable

[TriumphR3]

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?173-1227747-to-16197427-Conversion-PCM-Swap-with-Wiring-Pinout-Directions!

[maronielb]

This seems like to much work and I’m
Not good when it comes to wiring, what are the benefits on this swap anyway?

[ralmo94]

This seems like to much work and I’m
Not good when it comes to wiring, what are the benefits on this swap anyway?

Pretty much just a repin of the harness, shouldn't be too bad should you decide to go that way.

It's a more modern PCM than the ECU you have now, not sure, but should have a faster clock speed, and more ram? There are probably more people who are familiar with them than the ECU that you have.
Should be able to turn on highway mode for a lean cruise if you wanted.
More info here
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?303-16197427-PCM-Information-0D

To be clear I wasn't saying that you should or shouldn't go with that, but only pointing out that it is a fairly inexpensive option before burning the rig down.

Should you decide to do that, you can still use the same scanner and should be able to use the same aldl cable also. Should be noted that there are not any known factory bins for a 350 and a 5 speed for it, there are v6 i4 and 454 bins for a manual transmission however.

While I'm thinking of it, do you have access to another obd1 GM you can plug your scanner in to for throttle % ?

[ralmo94]

Just looked at your first picture of the scanner again, I noticed that the pnp or park neutral position is showing reverse
Does this always show this, does it change when you push the clutch in ?

[maronielb]

I think I’ll keep the computer that i have since i can run the correct bin on it and I’m definitely not burning the rig down i just spent 15k to restore it from the frame up. Yes my neighbor has a 94 I’ll plug my scanner into his truck tomorrow and see what it does

[maronielb]

No it doesn’t sometimes it shows drive/reverse and other times it shows p/n this does not change with clutch depressed or brake pedal depressed. It’s just randomly shows something each time i plug it in. However 90 percent of the time it shows p/n. My neighbors truck is an automatic so i will check tomorrow to see if my scanner changes when i put his truck in gear

[ralmo94]

Glad to hear. Too many repairable trucks end up in the scrap yard and are replaced with new trucks that aren't made as good. Well that's my opinion.

[maronielb]

I agree, I’ll sell my 2018 Silverado before i ever sell my 93, there just so well built, reliable, easy to
Work on and parts are cheap. Just sucks that there a bit hard to diagnose since they are Obd 1 but with those cables available that should solve that issue. I didn’t even know there was ways to pull live data on Obd 1 until
Like 1 month ago, that’s way i rushed to buy that scanner i taught i had found gold lol.
I’ll mess with the truck a bit tomorrow and get back to you on the scanner results

[maronielb]

So I hooked up my scanner to my neighbors truck, which is a 94 with a 5.7 L with a 4l80e transmission and not only does my scanner show a lot more information on his truck, but I was also able to verify that his throttle percentage at idle was 0% and his idle requirement was 713 and this is in park so that tells me that there’s no issues with my scanner but rather something going on with my truck so if there’s anyway that you can point me in the right direction at this point, I would appreciate that. Also I have attached the pictures of all the readings from my neighbors truck. He’s having issues with a strong exhaust smell /running rich I guess you could say so if you guys don’t mind looking at the pictures and letting me know if any of those numbers stand out to you that way maybe I can point him in the right direction to get his truck fixed thank you.

[maronielb]

197961979619796197971979819799

[ralmo94]

The more data is from the 7427 PCM, or equivalent service number.

I personally am wondering about the prom, if it's stock, or uncorrupted. Optimal thing would be if you had another prom to substitute for testing, but short of a trip to a u pull it salvage yard, kinda pricey to come up with one.

[ralmo94]

197961979619796197971979819799

Does he have any codes?

It appears it has been trying to lean the mixture to the extent it's allowed with a 111 BLM or long term, and it's open loop, short term is 128, 128 - no adjustment. Scanner says it's rich. Did he possibly crank his fuel pressure? O2 sensor health?

[maronielb]

He rebuilt the throttle body not to long ago but he used a stock rebuild kit so the fuel diagram is not messed it, also truck has a new fuel pump. O2 has not been changed, truck sat for years before he got it recently

[maronielb]

I see, would i be able to put a 7427 in my truck? Where would i be able to get a prom? My truck has a reman computer in it but i opened it up and the BCC code is correct for my truck but I’m
Not sure if they swapped the prom from the old computer into this one or if this reman unit came with the prom
Already in it. I just want a 700 rpm idle is that to much to ask for lol

[ralmo94]

He rebuilt the throttle body not to long ago but he used a stock rebuild kit so the fuel diagram is not messed it, also truck has a new fuel pump. O2 has not been changed, truck sat for years before he got it recently

I would check fuel pressure. They make a special gauge for TBI that goes between the return line and the TBI.

[ralmo94]

I see, would i be able to put a 7427 in my truck? Where would i be able to get a prom? My truck has a reman computer in it but i opened it up and the BCC code is correct for my truck but I’m
Not sure if they swapped the prom from the old computer into this one or if this reman unit came with the prom
Already in it. I just want a 700 rpm idle is that to much to ask for lol

Certainly not to much to ask for. Lol.
Yes you can swap a 7427 if you would like, you would need a PCM, the two connectors and a memcal, and a chip to burn, I don't recommend using a memcal adapter long term, instead solder the new chip in place of the stock one. Should you choose to do that, I could give you a memcal with a chip soldered on it if you send me a memcal. As far as getting a prom for the ecm you have now, pull it yourself salvage yard, and eBay are the only places I know of, you would need to find a manual V8, around here most of these trucks are pretty picked through in the yard.

[maronielb]

Ok I’ll let him know. I realized that earlier to suggest the pcm swap. Sorry for asking that question. I found a guy on eBay that can burn me a new prom chip but i have to send him the BIN file. Should i send him the BIN file that came with my truck or should i send him a BIN file for a 95 Silverado 5.7l with a 5 speed?

[MO LS Noobie]

On your neighbors truck the IAT (intake air temperature) is -40. This will make it run rich and indicates either a bad sensor or more likely the sensor is unplugged.

[ralmo94]

On your neighbors truck the IAT (intake air temperature) is -40. This will make it run rich and indicates either a bad sensor or more likely the sensor is unplugged.

TBI does not have IAT, or MAT. It uses engine coolant temp.

[maronielb]

Exactly! I was surprised that was even showing up on my scanner

[maronielb]

Ralmo94, when i order my new prom chip should i send him the bin file for my truck or send him the bin file for a 95 silverado with a 5.7 and 5speed? The computers are the same as far as the 7747 goes so would the newer bin file help out at all in terms of running better/showing for info on my scanner? If not I’ll just stick with my factory BIN which is AZDR

[ralmo94]

Ralmo94, when i order my new prom chip should i send him the bin file for my truck or send him the bin file for a 95 silverado with a 5.7 and 5speed? The computers are the same as far as the 7747 goes so would the newer bin file help out at all in terms of running better/showing for info on my scanner? If not I’ll just stick with my factory BIN which is AZDR

As far as I know, your ECU will read any prom with the same mask, I had been told previously that the releases of new BCC codes were incremental meaning Ab superspeeds AA. But I have also been told that sertian releases were to cure specific tsb's.

I would run the latest release bin for your mask that is correct for your combination, 350 with a manual.
Another member on here has better understanding of the different releases, if. I remember correctly it's @oneprojecttoomany


You might also send a pm to cottonpicker, he doesn't reply to threads, but he may be able to help you

[ralmo94]

As far as I know everything is in the bin for it, just have to add pins to the PCM connector and install one if wanted. Some have, and it is said to be better with a MAT rather than IAT as it's a heated intake

[maronielb]

I see, i don’t think my neighbor cares to install one, he just wants to fix his truck. It’s probably his 02 sensor honestly

[maronielb]

Cool, i was looking at getting the BIN for BDUY burned since it’s the newest BIN with the same mask as mine that i was able to find on this website, i wanted the BIN for a 95 but it wasn’t available for download in the bin file section

[ralmo94]

I see, i don’t think my neighbor cares to install one, he just wants to fix his truck. It’s probably his 02 sensor honestly

If it smells rich out of the pipe and the O2 is saying it's too rich, I'd say there is a rich condition, and replacing the O2 is kinda like shooting the messenger.

That's why I suggested checking the fuel pressure, if it has been cranked by a previous owner, that could make it run rich. An injector not closing could also, another thing that could cause rich condition is coolant temp, but it was reporting operating temp, so that's unlikely.

Only other thing I can think of that would cause it to be too rich, is if someone has put larger injectors in it, perhaps from a 454.

I usually approach diag with what easiest and cheapest first, at this point the fuel pressure would be easiest to check on his truck, and I think O'Reilly has a rental tool that would work, I have used one before, also making it cheap.

[ralmo94]

Cool, i was looking at getting the BIN for BDUY burned since it’s the newest BIN with the same mask as mine that i was able to find on this website, i wanted the BIN for a 95 but it wasn’t available for download in the bin file section

As far as I can tell it's for a 350 manual trans and the right mask, I don't see why it wouldn't work.
:rockon:

[maronielb]

i will let him know, hes mechanically inclined but hes old school he likes carbs, he doesnt really like dealing with anything that has a computer

[maronielb]

i made the purchase, i should have my new prom chip by next weekend, fingeres crossed this fixes my issues.

[ralmo94]

Any updates?

[maronielb]

Hi i received the new prom chip on Monday but i have not had time to install it yet. Wheather been shitty, i will probably install it this Saturday. One thing i was thinking about the other day is if i do the IAC reset but leave the IAC unplugged then the truck shouid idle at the base idle speed correct? With the IAC unplugged the computer won’t be able to get the idle up to 1k. This will also be a dead give away to is there is a vacuum leak present. With IAC fully extended out and left unplugged the truck would idle at the base idle that was set at the factory since the cap has never been removed on this TBI. Should i try this before i switch the prom chip? Or am i just running in circles

[ralmo94]

With the IAC closed and unplugged, yes it should run at where ever the butterfly stop is set, but that still wouldn't tell you why the ECU is requesting 1k idle speed. It may be a worthwhile test to see if it will idle slow, but if it has a vacuum leak, butterfly open too far, it should still target around 550 to 650 rpm, after warm up.

[maronielb]

Ok i get what your saying, i won’t be able to install the new chip
Until Monday evening but I’ll let you know what happens. I really don’t think it’s the chip i think it’s something to do with the TPS sensor but idk

[maronielb]

OK so I installed the new chip in the computer today and I did not notice any difference in the idle speed or the way the truck ran or drove. I didn’t notice any difference the RPM needle still sits right around 1000 RPM and also ended up breaking one of the little pins on my old chip when I was trying to take it out of the casing so I can no longer use that. So now I’m stuck with the new one which is fine I mean the truck still runs the same exact so I’m sure it’s not gonna be an issue but when I took the old chip out I did notice that it said Delco on it so I’m assuming that that is a factory chip that was never modified or anything like that but yeah, I’m gonna lost now with this with this idle speed. I don’t know what else to do frankly, I mean I can try a new TPS sensor just for the hell of it but other than that, I really don’t know where else to look.

[MO LS Noobie]

Go to beginning of your post, start there.

[Resin]

Do you have your scanner hooked up constantly as you are testing?

Edit: I read more of the thread and answered my own question.

Check for resistance across pins A and B of your ALDL connector.

[maronielb]

You are essentially tell me to adjust the base idle speed manually lol

[maronielb]

I don’t have a multi meter to get resistance, what wouid that do anyway?

[Resin]

Some GM ECUs have a factory diagnostic mode that requests a constant 1000 rpm regardless of other settings. Putting a 10k resistor between pins A and B will activate it. If your wires are worn and shorted to each other that could cause the ECU to enter that diagnostic mode and then it doesn't matter what you do, you will never get it to idle less than 1000 rpm. You can disconnect the IAC and set base timing but the moment you reconnect it, it will go right back up to 1000 rpm.

[TriumphR3]

A and B should have open loop between them, Yes?

[Resin]

Correct. Normal operation is open loop.
0 resistance puts it into a diagnostic mode that will flash the SES light.
3.9k resistance is another mode (I don't remember what this one does at the moment)
10k resistance is end of line factory test mode

[maronielb]

That makes sense but if the wires were shorted together wouldn’t they cause the SES light to constantly flash also aren’t those the pins that you jump to get the IAC to go fully closed?

[Resin]

If there was a short through a thin medium it could add resistance between the wires.
It could also be that someone wired a switch in somewhere to put it in diagnostic mode and they did a shoddy job.
It could also be, since I believe one or the other of the A & B pins is a ground, that the wire is worn and grounding on the body but the connection isn't good enough to be a low enough resistance for the base diagnostic mode. I believe it's something like 500 ohms or below is the threshold.

0 resistance will cause the IAC to close fully. That is part of that diagnostic mode.

[maronielb]

I had the whole dash harness out of the truck and i did not noticed any cut or spliced wiring or any switches, i don’t think the issue is in the wiring to be honest, the computer in the truck is a reman so idk if the computer itself is possible the problem? Or maybe it’s something completely unrelated that’s causing the idle to be 1k and it’s just a coincidence that the computer is requesting a 1k idle when i have my scanner hooked up

[Resin]

I'm not sure, but I had a similar problem and that's what it was. In my case, I had my ALDL connector for data logging connected. To connect to my particular computer, I need to use a 10k resistor. If I don't disconnect the resistor after connecting to my ECU it will idle at 1000 rpm.

I went through a lot of the same steps. I reset base timing, reset IAC so it was at about 15 counts, and set my TPS to .55 volts. After I hooked my data logger back up, it idled at 1000 rpm again and I lost my shit. I tore through every hose and nook and cranny and found a small vacuum leak. I thought I was triumphant having fixed it only for it to continue to idle at 1000 rpm after I started it back up as if to give me the middle finger. That went on for a few days. At one point I had started it and then hooked my data logger up and noticed a jump in rpm. TBIs kind of idle high from cold anyway but I thought it was weird. Once it was warm i disconnected the cable and the idle didn't come down so I shut it off and restarted it to see if it would jump again when i reconnected it. It started to idle normally for the first time. Then I connected it again, and right back up to 1000 rpm.

[Resin]

You can test your ECU but it would require you to adjust your manual idle control.

If you jump A & B or otherwise plug the IAC and adjust your manual screw to idle at about 600 rpm, the computer can't do anything about that.
If, when you hook the IAC back up or unblock it, it jumps to 1000 rpm again, you should see the IAC open farther and the computer would be commanding that. If it stays at 600 rpm, your throttle plates are open too far and your scan tool is lying to you.

[maronielb]

Sorry i don’t think I’m understanding what your saying, your saying if it stays at 600
My scanner is lying to me? Can you please elaborate? How would it stay at 600 if once i plug in the IAC it should idle it up to the target idle speed set in the chip. Which in my case would be between 650-700 once fully warmed up. If i plug in the IAC and it goes right back to 1k then i know Forsure that the computer is the cause of the 1k idle and not a vacuum leak/ wrong manual setting

[Resin]

You are right, it would open up to whatever idle speed is set to in your chip, but the point is, it wouldn't go all the way back up to 1000.
If it does go back to 1000, then it's something in the computer. If it starts to idle normally however, your scan tool reading a requested idle of 1000 rpm is not true and you know that the scanner is not giving you the right information. If the computer is truly requesting a 1k idle, that is where it will idle if it can. The only real way it has to achieve that is by allowing more air through the throttle. The only way it can do that is through the IAC. If with the IAC all the way closed and disconnected you are still idling at 1000 rpm, there are really only two possibilities. You have a vacuum leak, or the throttle plates are open too far.

[maronielb]

Ok yes this makes sense, so as of right now it looks like i have to adjust the base idle with the IAC unplugged and then see what it does after it’s plugged back in. I mean unless you have another recommendation? I just want this thing to idle at no more then 700 in neutral (truck is a 5 speed)

[Resin]

Run engine til it's warm. Shut it off and jumper pins A and B. Turn key on, do not start. Wait 10 seconds, and then unplug the IAC. Confirm It has closed all the way. You should be able to see the tip if it through the top of the throttle body. Turn key off. Remove jumper across A and B. Start engine and turn manual idle adjustment screw counter clockwise until the idle comes down. Check to make sure that the throttle shaft is actually resting on the manual idle adjustment screw and it isn't bound up in the body of the TBI. Now you should be idling in spec. Shut off and reconnect IAC. Restart engine and see what it does.

[maronielb]

Is there a way for me to read my rpm’s digitally while doing this? I can’t use my scanner because when it’s in diag mode the rpm’s fluctuate. And i don’t really trust the factory gauge.

[TriumphR3]

19827 not sure if the pic went through, but yes, coming off the coil there is a white wire with a connector which was/is used for diagnostic tach purposes by gm techs. I used it when I changed my half moon gauges to the needle gauges with a tach. You just need an auxiliary tach. It will give you a true rpm. Oh cool it did.

[maronielb]

So any aftermarket tach will work? I would like a digital one instead of needle that way i get he most accurate number

[Resin]

Another option is to hook up tunerpro with an ALDL to USB cable with a laptop. If you can find a definition file for your ECU. That will give you the computer's reading for what RPM the engine is spinning digitally.

[maronielb]

I just bought a digital tach from eBay, once i hook it up i will do the base idle adjustment and see what happens. I was going to buy a aldl cable but the manufacturer never got back to me on my
Question about the cd/usb that comes with the cable so i never purchased it. My
Laptop doesn’t have a cd drive and the usb option was on back order. I do have the ADX file for my
Ecu to be able to see live data on tuner pro i just don’t have a cable

[TriumphR3]

This manufacture has a thumb drive with there cables. I was in the same boat, no cd drive. It’s where I got mine.
https://obd2allinone.com/products/aldlobd1u.asp

[maronielb]

Hi guys, i know it’s been while and honestly i haven’t even messed with the idle i just gave up On it for a bit to finish up the truck but i did get an aftermarket RPM
Gauge so once i hook that up i will be able to see my rpm’s digitally and get a better idea of what the idle Actually is. I did notice something very wierd though, i got my ac charged recently and when the ac is on, the trucks idle drops, as soon as the compressor kicks off it increases back to right around 1k, isn’t it suppose to be the opposite? I taught the ac being on will increase the rpm?