I recently bought a 1991 fox body 4 months ago and was told the motor needed a rebuild or a stroker kit installed, the motor smoked real bad, I bought a nice looking fresh 302 5.0 off craigslist, the motor has a 97 explorer intake and plenum. I took out the old and put in the new, bought a gasket for the plenum, tightened everything down and plugged in, first time starting it up the headers turned so hot in 30 seconds they looked like they were turning to slag, I was told timing and vacuum, the timing was way off and their was some vacuum leak, corrected this issue and started it back up, sounded good but still really hot and a idle at 2500 rpm, narrowed it down to IAC, I didn't have cash at the time i placed the IAC in a can of gas for couple hours and shook the piss out of it to clean all the gunk off the valves that are inside IAC, after this it idled at just under 1000 rpm, and now it takes about 5 min for the headers to start glowing, this car had nos hook ups and an extra ECU in the car, it is currently hooked up to an A9S the original is A9L which is unhooked, I am not a mechanic by far and can't afford one, which is why I'm here, I need some 1 on 1 help please!
Have you checked the ignition timing with a timing light?
What sort of vacuum are you getting at idle?
What happens to the idle if you unplug the electrical connector on the IAC? Does the RPM decrease or remain the same?