Code 35, IAC Valve and high idle. - First Generation Forum

Forum Post / Reply
You must log in before you can post or reply to messages.
Code 35, IAC Valve and high idle.
Saturday, December 26, 2015 12:57 PM
Hello again everyone!

I'm back with the same 87 Skyhawk Wagon, 2.0L OHC Vin K. 101k-ish miles.

I'm having trouble with an erratic high idle... Long story short, I was driving it to the parts store perfectly fine, and when I went to leave, the car started to idle at full throttle.

I had thought it was the timing belt (as it was old and a bit loose) so replaced that, and the idle was lower, but still not fixed. I replaced a bunch of filters, the PCV valve, checked for obvious vacuum leaks, but not much seems to be working. I eventually got a code 35 from a paper clip in ODB port, flashing the CEL light for an "Idle Air Control Valve Fault".

I took out the IAC Valve, cleaned it (it was covered in gunk), and problem was solved (or so i thought). I drove it a couple miles, and everything was fine; it was running great. Once however it cooled down though, if started cool or cold it will go back to a very high idle UNLESS I get it above 30mph.... but this involves essentially neutral dropping the thing, which I would prefer to not do, as I'd like to keep my transmission in one piece.

So i went out and bought a new IAC Valve (AC Delco so it was exact) and slapped it in. It is doing the same thing... very high idle unless I get it up to speed, at which it will drive perfectly fine until I turn it off for 30 mins+. It also seems to surge up to a high idle. It will start at ( I dont have a tach sadly) lets say 2000rpm, then in waves climb to 2200, 2400, 2600, and so on until I just turn it off.

I am also still getting GM Code 35, "Idle Air Control Valve Fault" even with the new IAC Valve.

Do you guys have any thoughts at to what would cause this? My only other thought is to clean the leads on the connector if it has a faulty connection? Is there a fuse or relay controlling the IAC? What else would cause an "Idle Air Control Fault" with a brand new IAC valve? Is there a way to check against the valve by unplugging it while running? I know quite a bit about cars, but nothing this intricate as diagnostics on IAC's.

Thanks for any input! You guys rock.

Re: Code 35, IAC Valve and high idle.
Saturday, December 26, 2015 1:29 PM

I may have solved my own problem via youtube, but as it took forever to find, I'll leave this is a PSA to anyone who replaces their Idle Air Control Valve.

Apparently if you replace the IAC Valve you need to reset it via these steps:

1. Set the key to On (don't start)
2. Wait 10 seconds.
3. Unplug the IAC wiring harness.
4. Turn the key to Off
5. Wait 10 seconds
6. Plug in the IAC wiring harness.
7. Wait 10 seconds.
8. Start vehicle.

I had to feather the throttle for about a minute until it learned where Idle was, but it is now running fine again. Go figure.

I'll keep you guys updated if it continues to resume a high idle, but for now all is well.
Forum Post / Reply
You must log in before you can post or reply to messages.


Start New Topic Advanced Search