IAC

[BigBOB]

I know ya'll are probably tired as hell about hearing about IAC's, but i just replaced mine and now it won't idle below 2900 rpm. The throttle linkage looks fine and I couldn't find any obvious vacuum leaks. My truck is a 99 SOHC. It had been idling horribly in the mornings and once it got hot would not idle less than about 1200 rpm. I figured it was stuck closed when cold and stuck open when hot. I just don't know what the **** to do. I may go out there in a few minutes and put a few 12 gauge slugs through the intake and really give it a vacuum leak!! Any ideas at all would be AWESOME!!!

 

[Robb]

Re-set the computer?

 

[BigBOB]

Yeah, I had the negative diconnected for about forty-five minutes... I just got back from messing with it again. I unplugged the IAC and it idled at 2000 rpm. I plugged it back it and it idled at 2000 rpm. What the hell is going on? I guess there must be a vacuum leak some where. Thanks!

 

[Billy177]

make sure it is plugged in it may be defective or the prolblem isn't your iac it is your tps

 

[dogfriend]

Originally posted by BigBOB
Yeah, I had the negative diconnected for about forty-five minutes... I just got back from messing with it again. I unplugged the IAC and it idled at 2000 rpm. I plugged it back it and it idled at 2000 rpm. What the hell is going on? I guess there must be a vacuum leak some where. Thanks!

A couple of things to check:

1. Throttle plate stuck or otherwise prevented from closing completely. This would pass too much air at idle and prevent the IAC from controlling the idle speed.

2. Unmetered air (vacuum leak) somewhere past the throttle plate (leaking intake manifold). The most likely spot would be the lower intake manifold o-rings, which is a common problem for the SOHC engine. Search for 00M12.

3. MAF sensor damaged or otherwise reading incorrect air flow.