Odd Idle Issue (7A-FE), Idle increases in neutral - weirdest problem you will ever hear Options

[Espo]

My 96 ST Celica seems to have brought me a slight issue this winter - keep in mind this only starts happening when it gets cold.

Randomly, when I'm driving, whether it's city or highway, and I come to a stop in neutral (I have a manual transmission) my engine idles at 1200 RPMs...then climbs up to 1700 where it sits usually. On a few occasions it has climbed to damn near 2000 rpms.

Odd solution? If I punch the gas quickly it drops back to 1100 or the standard 900 rpms and stays there. Again, randomly, but it picks one of the two. Also, if I shut the car off and turn it back on, the idle returns to 900. I'm wondering if an idle speed control valve went bad, or a temp sensor, or an O2 sensor, or the fact that maybe I'm running 93 octane without resetting my air/fuel mixture from 87 has something to do with it. I do have an intake on the engine.

If anyone has any suggestions that I haven't thought of (or wants to tell me which one it is) please feel free. I can't think for the life of me what it would be - I haven't tried pulling codes but my engine light isn't on either.

[lilgreenyoda]

Sounds electrical to me. A IAC valve wouldn't just open and close unless its getting a screwy signal. The fact that the group of occurrances happen at random encourages me to believe this as well. IE If it was a vacuum problem it would only get better or worse depending when the engine warmed up. Temp sensor could be sending the bad signal out. To rule out the AFM pull your battery off long enough to reset the ECU. It will build its own fuel maps over again from there.