Crazy Idle problem!

[mccarlin]

Im having a weird problem here and need some assitance.

First off let me start by saying im running an AEM and the tuning was not touched and has not changed in some time now.

My car has been running fine for a good year now with no issues. I blew a headgasket and had that replaced and since then is when everything started. When i drive the car for 30+ minutes in 70+ degree heat the idle jumps to 2K RPM's and stays there till the car is cooled down some. The coolant or car never gets hot, and this doesnt happen if its cooler outside, even after driving a while. I can watch my AFR stay at 13.0-14.0 during this time even if im not touching the gas, like the IAC motor is stuck open.

Like i said the AEM hasnt been touched, so it has to be something mechanical. Either something went bad or something wasnt hooked back up right with the HG change.

I was thinking the IAC motor or IAT sensor?!?! maybe one of them went bad or is going bad?? Its been fine all along, just weird this issue has started since the whole head gasket issue.

thanks

 

[SuperSleeper]

Does this only seem to happen when you have the AC running? Cuz the car will idle higher when it's on... just a thought.

 

[SpeedFreak03]

My guess would be either FIAV (http://www.vallotton.com/fiavblockoff.asp) or ISC/IAC (http://dmtalon.v8eaters.com/ISC.html). If the FIAV goes bad, it can hold the throttle plate open when it's not supposed to. The FIAV works like this: It has coolant flowing through it, and it has a wax pellet inside. If the coolant is cold, the wax doesn't melt, so the FIAV holds the throttle plate open a little (to accelerate warm-up). Once that coolant is hot enough to melt the wax pellet, the wax pellet melts and the throttle plate shuts.

If its the ISC/IAC (same thing, just two different names, Idle speed controller/Idle air controller), then the idle can be too high or too low. My guess would be the ISC, they tend to go bad.

 

[SpeedFreak03]

Does this only seem to happen when you have the AC running? Cuz the car will idle higher when it's on... just a thought.

FYI - if the ISC is functioning properly, the idle will always be 700-800RPM, no matter if the A/C is on or not. The only time it would be higher than that is if the FIAV is holding the throttle plate open to accelerate warm-up.

 

[mccarlin]

Ive thought it might be the IAC motor control but i havent tested it or swapped it out yet.

like i mentioned, if its under 65 degrees i can drive all day and the car is fine, when temps get higher and i drive for 30+ minutes, then it starts to happen. Car is not overheating, and my AFR's go to 13.-14. by themselves and if i let off the gas, the car will basically drive itself. RPM's have risen as high as 2200 just sitting there at a light, you can hear the BOV whisteling the whole time, its pretty embarassing.