Help with sporadic high idle

This one is driving me nuts! I've been working on getting my VE table in line and making good progress but my idle will sometimes be ridiculously high when I come to a stop. I've just noticed today that when this happens the sensor data in TP shows idle mode to be off idle. My TPS data show 0.53 volts & tps% 1 or sometimes 0.51 & 0 with VSS @0, but IAC counts sometime as high as 100. When it does work properly, I've seen it go to idle mode as soon as VSS is below 4 and the IAC counts drop to 10-15. I have short logs of when it does both if anyone can help, this is a 7747 with $42 mask.

Thanks,Chris.

Post a log and your bin. Also what bin did you start with?

The TPS% is just a calculation from voltage in the $42 ADX file. There is no TPS% in data stream so don't get hung up on it.

But the TPS voltage is accurate and if it's changing? Have to fix that. Sticky cable? Worn shaft? Loose TPS? When key is turned on the ECM set's to 0% TPS based on voltage. So if voltage is changing then the ECM thinks TPS is open/off idle!

The '7747 doesn't auto zero like P4 ECMs, this is why the TPS is adjustable on vehicles that use the C3 style ECM.

I heard that somewhere too! Maybe a thirdgen thing? But none of the 7747 vehicles I've seen have adjustable TPS. And I made a hack to include TPS% in data stream to prove they do set to 0% after a throttle blade adjustment and then key on.

Odd, EVERY single 7747 and similar equipped TBI truck I have worked on had an adjustable TPS.

I've also had issues when the TPS was set just a tad too high as well.

Started with stock ASDU from this site. I thought that under a certain Tps, like 1.1.......Holly %@#&! I think I may have found the problem looking to tell you that value. How about "IAC TPS percent for closed throttle" being set at 99.21. Ha, that might have a slight effect huh? But then again why would it go in idle mode half the time?

Thanks anyway, hope that was the problem. Will find out in the morning,Chris

Like I said, my Tps will set on either 0 or 1, so I don't think it zeros out. In fact, after setting my min air I had to move my TPS. I enlarged the holes not enough the first time and went back to make them larger.
In between that I disconnected power every time thinking the ECM just needed to clear out. the first time I did that it came back up with the same value of 3% throttle. The second time around I realized the washers on the bolts were up against the TPS stopping it from moving. Once I cleared a little room for them I was able to get it set to zero.
Chris

Okay, scratch that. I must have some how keyed that in when I pulled it up. I went to close the window and it asked to save change. I said no, reopened and it's set at 1.17. So it looks like I still have a problem(besides being a dumb a$$!)

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Originally Posted by EagleMark

The TPS% is just a calculation from voltage in the $42 ADX file. There is no TPS% in data stream so don't get hung up on it.

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Read ^^^ this ^^^ !

"TPS from hack" is not accurate unless you have applied the hack to the bin being used during datalog.

TPS% Calculated from voltage is not accurate, just a calculation from voltage.

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Originally Posted by Six_Shooter

Odd, EVERY single 7747 and similar equipped TBI truck I have worked on had an adjustable TPS.

I've also had issues when the TPS was set just a tad too high as well.

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Really? I'd say it's a Canada thing but my truck was made in Canada and no adjustable TPS?

Long ago I read a post from Dimented24x7 that said TPS voltage was not an issue until over 1.0 volt... I did some testing with the TPS% hack so it was accurate from data stream and did find issues with anything above .74 so I don't even bother adjusting TPS voltage anymore unless over that.

Next time I work on one I'm going to revisit this though...

Nothing in your data log will help with a error 51 set! Plus there are other errors as well. Clear them and see if they come back. If they come back fix them.

Nice work on Fuel VE tables! :thumbsup:

But this thing has very low MAP kpa at idle? Hope it's a big cam?

So then the 1.17 is volts and anything under that with no speed should put me in idle mode?

Chris

Sorry, I did not see that. I guess I just thought no check engine light= no codes. I'll take care of that, thanks.

Chris.

1.17 sounds so familar? Where are you finding this?

But right now you are off idle always....even at .51v. I've never been able to do anything correctly with a Error 51 set so this may be the issue as well as Error 22 and 33.

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Originally Posted by Sla90lx

Sorry, I did not see that. I guess I just thought no check engine light= no codes. I'll take care of that, thanks.

Chris.

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It's a trick! :laugh:

First thing I do before recording a data log or with looking at data logs is look at error codes! :rockon:

It's scalar IAC - TPS percent for closed throttle

Right, but you said volts and it's 1.17 %.

First thing is get rid of error codes, then try data log again.

Cleared codes and went for warm up drive. wasn't idling as high but still no idle mode.

Chris.

That is strange? I just looked at some other data logs and it was working! Never have dealt with that before and not sure where to look for issues? Maybe someone else has an idea?

Anyone else have an idea what to look for? Everything I see in datalog is shows it should be in idle mode but its not. When it does go to idle mode the IAC drops down and runs about 700 rpms. I've even been setting in gear and have seen it go in and out but don't see any related values vary with. It's got me stumped.
Chris.

I thought that flag was based on TPS and VSS? But it may be more? Looking at yourt data... again... it does not look like idle data of a stock engine?

You never answered this?

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Originally Posted by EagleMark

But this thing has very low MAP kpa at idle? Hope it's a big cam?

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Unless that engine has a big cam change? Then something is wrong as idle is 60 MAP kpa... stock is closer to 35 MAP kpa.

If it has a cam? Look at this bin, it is your bin with more spark at idle, more RPM at idle and BLM cells changed to reflect engine/cam changes. Learn to use the compare featuer of TunerPro to find what I did. These changes will get idle more under control and lower MAP kpa when in idle and hopefully see you Idle flag work right.

Thanks, ill take a look. The motor is totally stock except for cam wich is probably overkill. .216 .223 @ .050. I know mechanically its solid with new everything except knock sensor and esc mod. But from day one this thing has been a dog with no throttle response what so ever and about ten mpgs. I know the timing has got to be part of my problem but I haven't really fooled with that yet wanting to get ve straight first. I feel I'm at that point. This morning's log looked damn good +/- 2 blms.

Chris.

I see that you changed the blm cells more around my idle. Would you explain those two as there is no parameter comments for them.
Chris.

map mph thresah hold and there is another mph threash hold but I forgotet, their scalers,mph trhes hold for idle.

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Originally Posted by Sla90lx

Thanks, ill take a look. The motor is totally stock except for cam wich is probably overkill. .216 .223 @ .050. I know mechanically its solid with new everything except knock sensor and esc mod. But from day one this thing has been a dog with no throttle response what so ever and about ten mpgs. I know the timing has got to be part of my problem but I haven't really fooled with that yet wanting to get ve straight first. I feel I'm at that point. This morning's log looked damn good +/- 2 blms.

Chris.

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With that cam and stock chip it should be a dog and your lucky your getting 10 MPG!

Well with the spark I added for idle it should be much better with that cam at idle only. Now I know you have been working on VE and done a great job on the table. But after you get a complete spark table adjusted for performance and that cam? It will need to be done again.

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Originally Posted by Sla90lx

I see that you changed the blm cells more around my idle. Would you explain those two as there is no parameter comments for them.
Chris.

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BLM is Block Learn Mode and is Long Term Fuel Trim. It's set from INT = Short Term Fuel Trim. With that cam your overlapping the learned cells or not even in the right cells. Take the MAP and RPM and create a ... never mind, look at this.

And ony is probably correct in that a MAP threshold for idle is not being met. With the little RPM and lot of spark I added at idle the MAP should get a lot lower.

I understand blm and int are short and long term. What I don't know is the meaning of cell boundaries. Can you point to some threads that explain this in depth? I agree with Map threshold for idle but have not found anything in the bin yet to support this. I am committed to learning this and know that it will be a long road to travel. I fully expect to make hundreds of changes before all is said and done and am up for the task. I've even purchased both a Greg Banish's books and have enjoyed them so far(thanks for that one.) I'm about to go for a drive and see how these changes affect things.

Thanks, Chris.

Never mind the request, finding plenty info out there. Google is my friend!

Chris.

Just an up date on idle mode. I bumped TPS% for idle up to 3% from 1.17 and haven't had a problem with staying in idle mode since. My BLMs are consistent 27-28 cruising from off idle to 75 on hwy. I need to drop fuel at idle now with the BLM cell boundary changes but I don't think that will take too long. So it looks like next up for me is to start playing with the timing I guess.
Thanks for the help, Chris.

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Originally Posted by Sla90lx

This one is driving me nuts! I've been working on getting my VE table in line and making good progress but my idle will sometimes be ridiculously high when I come to a stop. I've just noticed today that when this happens the sensor data in TP shows idle mode to be off idle. My TPS data show 0.53 volts & tps% 1 or sometimes 0.51 & 0 with VSS @0, but IAC counts sometime as high as 100. When it does work properly, I've seen it go to idle mode as soon as VSS is below 4 and the IAC counts drop to 10-15. I have short logs of when it does both if anyone can help, this is a 7747 with $42 mask.

Thanks,Chris.

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It's possible the VSS signal to the ECM is > 0 MPH when the problem occurs. That can occur with loose wiring, poor ground, etc. Bottom line, for most OBD1 ECMs VSS must report absolutely 0 MPH or will not be considered at idle. The fact that is works sometimes and not others indicates a possible inconcistent VSS reporting issue to the ECM. Additoinally, most code has a minimum TPS value that determines when idle is being considered. Might check that value. For example, for '7730, it's 0.78% and below.