I have a 1990 mustang gt that has intake, pullies, headers, CL mass air for 19 injectors, and TB. When ever I plug in my IAC the car revs up to 2k and 3k rpms but when i unplug it it idles somewhat normal at around 800 rpms. Help!
Did you recently replace or remove the throttle body? If cleaning the idle air doesn't change anything, I would look at the TPS first, if it is on check your throttle body for the adjustment to your idle. Once set, you will have to re adjust the TPS again.
Does it reset itself if you key off and restart ? I just had this problem out of the blue. I cleaned my ten pin connectors and replaced my 20+ year old TPS sensor. No high idle after that. Start with cleaning the IAC as mentioned.
Has the IAC been replaced? Is it possible the idle set screw was opened in an attempt to compensate for a bad IAC?
Consider that if the idle set screw is too high. With the IAC disconnected and no air at all through the IAC, the idle is a high 800 RPM. Therefore, even if the IAC duty cycle is ZERO, there is still too much air entering the engine.
The RPM's should drop or the motor die outright if the IAC is disconnected. There is either a vacuum leak, the IAC is bad, the idle set screw is too high (or a combination of all of the above).
What is the condition of the throttle return spring? The TPS (bad or misadjusted) has already been mentioned as a possible source of the problem. IMO, the idle set screw set too high may be adding to the problems.
WTF! today I go out and try to get to the bottom of my high idl, crank car and whoa! Idles perfect at around 850ish. Then I leaves in my truck and go to the store comes back cranks the stang and BAMMM! idling at 1800 again plus my blinkers (with new bulbs) stop working but the hazzard lights works. My car doesn't like me. lol
I wouldn't think the blinker problem is connected to the idle problem, unless you have general moisture problem that is getting into the wiring connectors and wreaking havoc. Have you cleaned your ten pin connectors (sometimes called salt and pepper shakers) located up near the rear of the intake manifold ? These connections control the injectors and pretty much all of the electronic sensors on the engine. They have some strong clips holding them together, but they need to come apart and be cleaned. Get some electronic spray cleaner and maybe some toothpicks or something to get down into the female parts of the connectors and clean them out good. Some people even bend the pins/clips to make better contact. After you've cleaned them out good, get some dielectric grease and apply to the pins before putting it all back together. Maybe this will help... It helped mine.