2001 Chevy Venture

Greetings, I have a customer that has a 01 Chevy Venture and has trouble idling and staying running. It's mainly happens when it's cold after it warms up it will stay idling by itself a lot better. The IAC valve has been checked and replaced with no help. The throttle body has been taken off and cleaned and I scoped everything I could with no visible problems. Idles way too low when cold but will stay idling after it warms up after about 15-20 minutes of running. I noticed on the scan tool it will slowly go up to maximum counts of 256 I think it is and stay there. I can get it to hover around a lower number for a little bit but when it starts going up because up all the way. What is that counts PID showing on the scan tool? is it just every time the motor is commanded to move? I don't know if that's an issue or not? I scoped both at the I act valve and the computer thought I had a problem with one of the coil wire's or computer as I saw Paul had on one of his videos but the next time I checked it it came out okay. Thanks for any suggestions, Doug

The IAC Counts can be a bit confusing. 0 translates to the valve all the way closed, and 256 translates to all the way open. So, your data indicates that the PCM is trying to raise the idle speed, and can't. I've got some example data from an '03 Venture here for reference:



How does the engine run off idle? Plenty of power? Mostly just want to rule out an intake restriction (rats nest in the intake tube, plastic bag in the air filter, like that). Once the engine warms up, what do the IAC counts do?

To me it seems like the engine is suffering from genuine lack of air coming into the engine when cold. You can confirm this by creating a controlled vacuum leak and see if the idle comes up. If so, I'd suspect the IAC still isn't opening correctly, despite being replaced. Do you have bidirectional control of the IAC with a scanner? You can unbolt it and command the IAC back and forth, see if it moves. DON'T bolt it back up without retracting the pintle.

Speaking of, has anyone replaced the throttle body or gasket recently? It's possible to get the wrong one (or install it the wrong way) and create this issue.

Hi Tyler thanks for responding! Customer said the throttle body was taken off and cleaned as well as another IAC valve installed of which I did, then put back the old one after no change and verified the old one was opperational while off and engine running and cleaned passage way while appart. Reinstalled and sprayed all around checking for intake leaks and found none. All I could find on my Autel scanner was the IAC Counts no other controls...but I will check again. I will also include my scope readings. My MAF and MAP reading seemed good also. It seems like the Autel should have some control PID... I like the way you sent all your info! My scanner, that I know of, won't save to send info like the Snappy can...can it? I'm still learning. Just got it and the Pico not to long ago! Waveforms to follow. Thanks again, Doug

As techs, we ask each other for outside opinions to make sure we aren't going too far down a rabbit hole (at least I do). That being said, I am not trying to de-rail the IAC discussion, but lets take a step back for a sec... Remember that IAC is an output of the PCM, so before we go too far lets look at the inputs. I have seen other things cause engines to idle low, and the PCM raises the IAC count just to try and avoid stalling. My point is that the IAC deal may be a symptom and not necessarily the cause of the problem. Hopefully that makes sense (I am a teacher and I tend to over-explain things).

The first thing I would look at is a custom PID list during those 1st 15 min, while looking at Fuel Trims, MAF, MAP, ECT, O2's, RPM, TPS. I know you said that you sprayed around for a vacuum leak, but with the cold start progressively getting better as it warm up, I cant help but think about a dried out or worn gasket in the induction system somewhere. Even if you dont have any external leaks, don't rule out internal vacuum leaks if it is a "V" motor with a lower plenum.

If you can grab some of those pid's during the event and then after it gets better, I would love to see them

Also, if you are using an AUTEL, make sure you grab these PID's in Generic OBD2 mode, not vehicle specific/enhanced. The live data has alot of discrepancies in the AUTEL from what I see every day in shops. The Generic OBD2 mode is much more accurate.

Yeah thanks a lot for that great info. Sorry it's been so long since I got back to you but haven't worked on the vehicle for a while. I'm going to this weekend and I'm going to take the throttle body off again and check to make sure that's okay as well as checking the IAC valve again. I'm pretty sure I was checking it generic mode on the scanner but I'll make sure that I do now with that great info for sure. I will get back to you all with my findings! This vehicle also has a bit of an overheating issue too but that's another fix to work on later. Thanks again, Doug

TheTechWhisperer wrote: As techs, we ask each other for outside opinions to make sure we aren't going too far down a rabbit hole (at least I do). That being said, I am not trying to de-rail the IAC discussion, but lets take a step back for a sec... Remember that IAC is an output of the PCM, so before we go too far lets look at the inputs. I have seen other things cause engines to idle low, and the PCM raises the IAC count just to try and avoid stalling. My point is that the IAC deal may be a symptom and not necessarily the cause of the problem. Hopefully that makes sense (I am a teacher and I tend to over-explain things).

The first thing I would look at is a custom PID list during those 1st 15 min, while looking at Fuel Trims, MAF, MAP, ECT, O2's, RPM, TPS. I know you said that you sprayed around for a vacuum leak, but with the cold start progressively getting better as it warm up, I cant help but think about a dried out or worn gasket in the induction system somewhere. Even if you dont have any external leaks, don't rule out internal vacuum leaks if it is a "V" motor with a lower plenum.

If you can grab some of those pid's during the event and then after it gets better, I would love to see them

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So I finally finished putting this vehicle back together. I had it apart again, re-checking the throttle body, EGR and IAC valve. Didn't find any specific problems, accept that the computer, once it pulls back the IAC valve, it doesn't seem to close it at any RPM speed until the ignition is turned off...?
The van stayed running a idle this time, although it was very low. I did find the idle speed screw, it is nice to have one, and raised it to 600+ RPM. It was down to just over 500. I found no abnormal scan PIDS on the ones you mentioned Tech, (BTW what is your name?). There is a strange vacuum like leak sound coming from under the upper intake, coil area but no significant, abnormal fuel trim values, except when I induce an intake leak. Trims are down at 0 to 2% and raise to 8 to 12 when induced.
One other ? I have is about the IAC

Darn computer, or I should say fingers...
Continued... IAC computer control ?. Is there some problem with the PCM not adjusting the counts up and down during running speed? Just wondering,
Thanks, Doug