Importance of the IAC

[subhumanzz]

I just finished installing a mast ls7 4500 efi intake and a fast 4500 tb. Upon start up i noticed a high idle condition which i assumed was a vacuum leak. I noticed that the tb blades were open a fair aount so i closed them up and I started looking and couldnt find any evidence of a leak anywhere but i took the manifold back off and reinstalled it again just to make sure all was well. So i hook up the scanner and notice that after the car warms up the iac is 0 the entire time. I am running nothing off of the manifold vacuum except for the map. there is nothing else on the car no ac, no brake booster... Cam is a .740 lift solid roller with etp ls7 heads and the new manifold. so i am wondering if the iac is even practical or even matters in my application? no street driving is done with the car either if that matters.

[WS6FirebirdTA00]

Yes it matters, it controls idle airflow. If it is at zero you have a leak somewhere causing it to stay shut or your TB is still open too far. Is there a hole in the TB blade? Is there poor sealing around the perimeter?

[sarg]

My tb actually came from the factory with a hole in it. If the car idles fine with 0 iac, what importance is the iac valve? Not being smart arse, honestly curious.

[WS6FirebirdTA00]

If the car idles with an IAC position of zero, chances are it is not idling properly. I would be willing to be the adaptive spark is always negative trying to pull the idle back down. The bottom line is the IAC is not having any control over idle and can cause some instability.

[Chris@HPTuners]

the IAC should be around 50 steps at idle, if it is zero you have a vacuum leak, the TB is open too far (set screw) or the throttle blade hole is too big (if it is stock, then unlikely).

[edcmat-l1]

It is a 4500 throttle body. Carb style, no hole. He got it working right.