how can you tell if the IAC is bad? just recently rebuilt an ls motor and the motor idle very weird up and down up and down during cold starts before the rebuild ........i rebuilt the motor after it blew the head gasket .....i finished the motor started it up and it idles up to about 3 grand and will not go back down....i'm sure this is my problem.... i pulled the intake and plugged the hole like i found on another tech post and the idle went down perfectly.....what do you guys think?

 

is their a check engine light? if not then im sure its a vacuam leak of some sort.

 

Are you sure it is the idle air control valve?

It could be your Fast Idle Valve. That is exactuly what happend to me. Mine would idle up around 3k, and then after it warms up it revs all by itself between 1-2K

You pluged the whole that is about the size of a nickle on the bottom half of your throttle body?

That would be from your Fast Idle Valve, not your IACV.

You don't really need it. But to get rid of the problem you will either need to replace it (something like $90). Or take it off and make a gasket that will cover up all the wholes in the FIV and bolt it back one. It will be like you don't even have a FIV. But that's not a problem, it will just take your car longer to warm up if you let it sit and idle until it is warm. That about the only down side I know of.

Good Luck!

 

you may also want to check the throttle position sensor they act in same manner but to get one go to import salvage yard the dealer only sells with throttle body so your lookin at 300.00/450.00 dollars. but as well check your fast idle valve that has also been culprit.

 

yes the sensor right behind the intake manifold whatever it's called with the 2 coolant lines going into it.......i took it out tried cleaning it but no go....i hope a new one works if you guys have anymore suggestions let me know asap! thanks