Bad IAC??
 

Recently my car has been idling high and surging when in gear, especially coming to a stop itll be around 1500 rpm with my foot on the brakes. Ill be completely stopped for a few seconds and the rpms will drop to normal then fluctuate up and down. I have been reading IAC counts on my scan gauge and ill see anywhere from 0-50 or so when im stopped. If the car is in park and I let it idle, itll surge a little bit as well. I unplugged the IAC when the car was running and and it ran normal at idle parked but if I do it before I start the car the rpms will shoot up to 2500. I checked for any vacuum leaks and couldnt find any, but Ill look again.

Iv also done a tps and iac relearn and it didnt change anything. I just put on a ported stock tb from Potz (ebay) and it seems worse than when i had the stock throttle body on. would this make a difference?

Any thoughts on if this is a bad IAC or something else?

check your PCV first....the ENTIRE hose....if the hose crapped out you have a major vacuum leak..........ask me how i know

ill look that over again. I actually replaced the whole pcv system not too long ago so its still fairly new.

Put a new iac in.....then go from there. If it was a vacuum leak it would be present all the time.

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Ill try that first. does unplugging the IAC while its running and it still showing fluctuating counts mean anything? I forgot to mention that in my op.

I'm no tuning or PCM expert.....but there's all kinds of weird things that go on with these PCM's when you think they shouldn't be.

Your problem could also be a failing or worn out TPS or failing or dirty MAF.....which will send bad signals to the PCM that will cause the PCM to send bad signals to the IAC causing it to open and close improperly.

These PCM's and sensors work well......but they are also a crap system because everything is so in depth and tied together that it makes diagnostics so hard sometimes.

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i ended up ordering both the tps and iac and im hoping thatll fix this issue...

Ill clean off my maf and see if that does anything.

just an update, I put in a new IAC and TPS and it solved the issue.

So I thought my problem was fixed but I guess not. I swapped iac and tps as well as replaced the pcv hose from the tb to the valve cover. After both things (done at seperate times) it seemed that the car was running normal when I was driving it but went back to the way it was the next time I drove it. I did the relearn when I swapped the sensors and disconnected the battery when I fixed the hose. Not sure if it makes a difference but when I found the hose, I had someone pull it when I had the car in gear and it idled fine. Can I block off this part of the pcv to see if it makes a difference?

dont forget the junction of the PCV behind the intake.........thats another place where it BREAKS !

I didn't think about that. Ill check that out. I might as well pull all of it out and change the pcv valve while I'm in there.

Well, I once changed out the IAC in my S10 for the same thing and it didn't fix it. Wound up replacing every single thing that has an effect on unmetered air or spark...EGR, TPS, MAF, MAP, PCV....wound up being the cheap ebay IAC I put in failed almost immediately. Took the throttle body off, cleaned the IAC orifice and the original IAC itself, reinstalled, and been running on the stock IAC ever since. Don't know about the LS1 but the older Vortec setup you had to measure the IAC when removing it and set the new one to the same height.

well i pulled my pcv and replaced the valve, as well as cleaned my maf and and it helped alot. it still surges but not as much. I have a stock tb coming and Im going to put that on and see what that does because i was told ported stock tb's can have this issue.