I have a '97 Ranger and that idols too high. When warm it idols at about 2K. I replaced the IAC with a new non-OEM part with no noticeable difference. When I disconnect, it, idol returns to a normal speed somewhere around 1K.
I've replaced plugs, PCV, coolant temp sensor (temp guage on dash is still perma-pegged at the bottom) air filter, new oil, and even the MAS, and still no change.
For a cold start, it starts and then oscillates from hi rpm to so low it sounds like it's gonna stall. If I cold start w/o the IAC plugged in, it starts fine (although it doesn't have the normal high rpm of a cold engine, it just starts and idles as if it were already warm)
So in summary, It runs fine w/o the IAC plugged in, but the check engine light stays on. Any help would be greatly appreciated.