Got a weird one, my car runs great and starts up perfect when the AC is off but when it is in the on position the car will start and stall immediately. Switch the AC off it starts fine. I replaced the ECM in the spring and had a new PROM but never did IAC relearn, could this be it? Also the IAC was replaced a year or two ago with a parts store IAC ( I know I should’ve known better), but I kept the original. I’m going to mess with it soon but was curious if anyone had any other ideas.

 

So......turn the A/C off before you start it. What makes you think you're supposed to start an engine with A/C on?...

 

You can "mess with" the original IAC if you like, or you can find the instructions posted here numerous times and disassemble, clean, lube, and reassemble it Unless the stepper motor coils are damaged, or the pintle/rack gears are damaged from neglegence, there is a reasonble chance that it will work as well as new once it is serviced.

 

Most cars are designed that the A/C clutch circuit isn't hot in crank anyway. I've never had a car that wouldn't start with the A/C turned on...

 

I may just have to deep clean the IAC or try the original IAC and see how that works, I really cleaned that TB a few months back but won’t know until I try. It’s a weird problem but not a big deal in the grand scheme of things but I still want to try to correct it.