Ridiculously high idle on startup
This just started this morning. Its a stock 93 5.0 with AOD. It was maybe 32*F outside, but thats never been an issue before. Perhaps the cold is finally getting to the old girl, i dont know.
Anywho, i turn the key and she fires right up but the rpms hit 2000 immediately and slowly got higher. The rpms usually hit 1700 or so and gradually come down as she warms up. So i shut her off and try again because this is NOT normal. Second start, same thing. Hits 2000 rpm immediately and slowly got higher. I feather the pedal and the rpms go up and the rpms keep climbing from there. I shift into D and the rpm immediately falls to 1000-1100, which is where it usually sits. I shift back into P and the rpms jump back up to 2000 immediately and slowly got higher. I shut it off and pop the hood. The throttle linkage and cable are not binding. The air tube is firmly secured at the throttle body and the MAF. I try starting a third time and the rpms hit 2000 immediately. Again, i shift into D and the rpms drop to 1000-1100. I shut her down and left her sit as i wasnt in a very trusting mood so my uncle let me borrow his truck instead of me driving the Mustang to work.
The only thing i can think of is the IAC, which is maybe 2 years old, Motorcraft. But since the rpms do fall when i shift into D, that would suggest the computer has control of the IAC, correct? Im just not sure why it would jump to 2000 and keep going when its in P. I have not tested the TPS nor the IAC yet as ts so blasted cold. Nor have i checked for codes. Right now im just looking for opinions.
Another observation is that last night after work, it took three tries to start. It was just as cold then. She cranked and tried to start, but wouldnt. I had to turn the key a little further than usual, too. On the third try it did the same so i feathered the pedal and she started (the last time this happened it was the PIP failing). The rpms did not hit 2000 last night like they did this morning. They were normal. Drove home no problem. Not sure if any of that is a clue, but there it is.
I do have a 1993 Ford Powertrain Control/Emissions Diagnostic Service Manual (the HUGE manual dealers used) i am currently looking thru in hopes of figuring this out, but so far nothing pops out at me. This particular issue doesnt seem to be covered. I also have a Breakout Box to go along with it...somewhere. Cant remember where i put it. Not even sure if it still works.