TPS causing throttle hang?

**1BadAction** · 09-03-2014

so I have a new ACDelco TPS, set to .5v, 20iac etc. I'm still having an issue where throttle closed reads .53 volts and I think that is causing my IAC to hang around 50 or 60 counts, which in turn makes the truck idle at 850-900 rpm instead of the desired 750-800... Could this be the problem, or possibly something else? I have no idle speed adders enabled that I know of.

**steveo** · 09-03-2014

i doubt it's the tps.

is your ECM using a self-bottoming tps that remembers the lowest tps setting as zero, or is it adjustable and meant to be set to a particular voltage?

if it's adjustable, the ECM should have a constant for voltage that equals 0% tps that you can modify....

what about your VSS, is it connected? is it aware the vehicle is stopped? perhaps you're stuck in open loop idle control and it's just adding steps?

is it even in closed loop idle logic when the iac 'hangs'?

**1BadAction** · 09-03-2014

Truck is all stock, not a swap. VSS and all electronics are hooked up as should be.

It's in closed loop idle when it "hangs", there is a 255 second delay until it goes into open loop idle (stock bin is OL idle) The ECM recognizes idle as anything less than 2.3% TPS and it is setting the idle flag when it's idling high. Also, worth mentioning is the IAC is also a new Delco unit.

I guess the thing that raises my suspicion is the TPS not returning to the same spot every time, and I can't find any mechanical slop in anything.

**fastacton** · 09-03-2014

You might want to try a different TPS and see if the problem goes away. It's not unheard of for stuff like this to be defective out of the box. It may not be the issue, but it's an easy thing to check and eliminate as a possibility.

**steveo** · 09-03-2014

or bump the throttle stop down a bit.. just a bit. see if it gets better with the tps in a lower range.

are you sure its actually returning to the stop? cable is free? plates dont get sticky as it warms up?

**1BadAction** · 09-03-2014

The original TPS did the same thing... I replaced it thinking it was a problem even though through the throttle range it was nice and smooth.

I'm going to fool with the throttle linkage and throttle stop tonight then take a look at the cruise control rod also. Will report back.

**brian617** · 09-04-2014

I believe whatever voltage the ECM sees at initial start up is what it will use to identify closed throttle. Make sure Key On Engine Off voltage is the same as the voltage you get when you push throttle then ease it off gently. May have to add a 1/2 turn in on throttle stop to keep blades from sticking in bore. Seems like I remember having this issue and I simply added a half turn in on stop.

**Fast355** · 09-04-2014

Originally Posted by brian617

I believe whatever voltage the ECM sees at initial start up is what it will use to identify closed throttle. Make sure Key On Engine Off voltage is the same as the voltage you get when you push throttle then ease it off gently. May have to add a 1/2 turn in on throttle stop to keep blades from sticking in bore. Seems like I remember having this issue and I simply added a half turn in on stop.

Actually on those older ECMs the ZERO TPS voltage will be the lowest voltage the system sees during the engines operation. I once had a .bin file get corrupted in a way that with the a/c on the engine would hang at 1,300 rpm after you moved the shifter to park. Ran fine as long as you were driving, the second you put it in park it would jump up and stay until you restarted. I finally fixed it by taking an untouched .bin, pasting in my spark and fuel tables, etc and never had another issue. If memory serves me you have to come up to almost 3% before it will turn the idle logic off.

**1BadAction** · 09-04-2014

Originally Posted by brian617

May have to add a 1/2 turn in on throttle stop to keep blades from sticking in bore. Seems like I remember having this issue and I simply added a half turn in on stop.

This is exactly what I did last night and has cured the TPS issues. .55v at dead idle, and goes back to .55v every time, no variance.

Unfortunately I'm still having this hanging problem. :(

Originally Posted by Fast355

I once had a .bin file get corrupted in a way that with the a/c on the engine would hang at 1,300 rpm after you moved the shifter to park. Ran fine as long as you were driving, the second you put it in park it would jump up and stay until you restarted. I finally fixed it by taking an untouched .bin, pasting in my spark and fuel tables, etc and never had another issue. If memory serves me you have to come up to almost 3% before it will turn the idle logic off.

This could quite possibly be the same issue as I am having. After my adjustment to the throttle stop, the idle is hanging at 950 to 1000rpm and IAC position will not back down when the AC is turned off. at the correct idle speed the IAC is around 25 counts, but after having the AC on, then driving around and parking, once put into park/neutral the counts will not go below 60, even when I turn the AC off. Turn the truck off and restart with no change and it idles at 800rpm correctly.

**steveo** · 09-04-2014

didja clear the ecm right off after you dicked around with the idle stop?

**1BadAction** · 09-04-2014

Originally Posted by steveo

didja clear the ecm right off after you dicked around with the idle stop?

Yes.

I checked a datalog... Desired idle speed is 775 after a drive with AC on, IAC vs coolant at that temp is 25, yet it still idles at 900 with the IAC counts over 65.

I'm starting to think there is something inherently wrong with these 7060 ECMs. This is not the only odd behavior I have noted. Its a damn shame, because right now the truck idles smooth as silk, doesn't ping, and runs extremely strong. If I start with a new ECM I'm going to need to do all this shit over again.

**steveo** · 09-04-2014

you must be hitting some weird idle logic if it's not bottoming the iac out trying to achieve idle target. are you sure it's in closed loop idle mode, and if the answer is yes, how do you know for sure? 'cause it really sounds like it isn't.

**1BadAction** · 09-04-2014

Originally Posted by steveo

you must be hitting some weird idle logic if it's not bottoming the iac out trying to achieve idle target. are you sure it's in closed loop idle mode, and if the answer is yes, how do you know for sure? 'cause it really sounds like it isn't.

It is in closed loop, with a 255 second "down counter" until it goes into open loop. The bin is originally an open loop idle bin.

Here's a screen cap of when it's acting up. This is in CL, no?

**brian617** · 09-04-2014

Alternator voltage looks a little low, have you got the AC on and blower on full blast maybe?

**steveo** · 09-04-2014

yeah, looks normal by the dashboard? but there may be conditions in the code where the 'idle' bit is set to 1 but it's still going open loop idle, not following the idle target, and it's just advancing a fixed number of steps, that seems to be what's going on anyway...

maybe it is a battery voltage thing? 12.1 might be in the range of 'oh crap, there's a bunch of battery voltage... lets add idle speed'?

is there any disassembly for this mask? (dont even know what mask it is, you haven't told us)