If the IAC was bad, the car should have been running rough at idle. Usually even if the IAC goes bad, the car will still run at higher RPMs.
You should scan the computer again and see if any codes popped up, even if the check engine light isn't on. You should also call some local shops and see if you have one near you that will only charge you if they find the problem. Tell them that a few people already looked at it and you don't want to spend more money without a guarantee.