Check ALL the bolts to the intake manifold. Air seeping past the gasket (ie vacuum leak) is the usual culprit of high idle.
Another trick is to get a propane bottle with a hose. Use a small amount of propane and probe around the engine and listen for an sudden increase in idle. That will be the location of your vacuum leak.
Also, before you change the IAC motor, remove it and give it a good cleaning. They can sometimes get gummed up.