I just finished replacing a head gasket over the winter, and I am greeted with a high idle. There are no new parts since last fall when she ran like a dream. I can watch the IAC count drop from 80 to 0 without having much, if any, effect on the idle speed, which is around 1500.

I have checked for intake leaks, visually and with carb cleaner; there are none. The throttle screw has been adjusted and verified, so there is no extra air coming past the blades.

So I guess I have pretty much narrowed it down to the IAC and the EGR valve. When I pulled the IAC, it looked like it was fully extended, out to about 1 1/8". Is this fully pegged? If so, that must mean I have a leak somewhere else, right? I'm pretty stumped.

Any ideas what it could be?

 

If the IAC is driving to "0" then it's functioning, and trying to maintain the commanded idle. You've most likely got a vacuum leak that you haven't discovered yet.

 

I have an identical problem. Its like it has to hunt for idle, if i let it sit for a couple minute and idle it will find it, and will return to it quicker, but still slow,


I plugged up the IAC hole in the TB and it still idled the same, so i know there is air getting in someplace but i cant find where.

 

I don't really ever find idle. It'll start out around 1000 and then work its way up to 1500, even with the IAC doing it's best.

So if Datamaster says the IAC is at 0, then that means the spindle is actually moving? I thought it might have just decided to not respond, even though the PCM is sending a signal to the IAC. Is there any way to test if the IAC is moving?

 

Block off the IAC hole in the TB, put the intake and stuff back on and see if the car will run. If it runs, then there is air entering the motor at another place.You should have to leave your foot on the gas a little bit to crack the throttle blades so air can get in.

 

I blocked off the IAC hole in the throttle body, and it was seriously struggling for air, so I guess even though I am not throwing a IAC code, and the PCM is sending a full closed signal to the IAC, it's not clsing properly.

I have a replacement IAC on the way from Dal. At least it wasn't an intake leak that I couldn't find.

 

The scanner is simply telling you what the PCM has commanded the IAC motor to do.... it does not have any feedback to tell it if the motor actually moved the pintle. Shoebox has a procedure for checking the IAC on his website, if I recall correctly.

 

You're right in that the PCM was telling the IAC to do something that it couldn't accomplish. So, I replaced the IAC and the high idle is gone. Now the IAC counts don't drop to zero, and I have a perfect 800 RPM idle. I am curious as to whether Shoebox's IAC test would have identified the problem, so I will keep you posted when I check that out just to see.

Thanks to everyone for their help. It's great to have a smooth-running ride for spring.