Sunday afternoon I noticed my 97 F-150 4.2 5-Speed manual had a higher idle. When the AC compressor kicks in, the motor revs up higher than normal for about 4 secs then comes down a little. If you barely press the accelerator, I mean just gently touch it, the motor revs up for 4 secs. Dont have a tach, but just idling in neutral, is about 150 rpms more, and when AC compressor kicks in, rpms jump about 300 rpms i assume. Maybe vacuum, IAC??? Plugs, wires, and normal tune up done about 2400 miles ago.

 

Also, no codes thrown yet.

 

Do the basics:

-Unplug battery.
-Clean the throttle body flap, and everything with carb cleaner / air intake cleaner.
-Remove the IAC and clean it with air intake cleaner as well.
-Re-assemble and plug battery back in.

If idle is still too high, inspect for vacuum leaks. Cleaning will often "fix" a sticky IAC, however in certain cases the problem returns and the IAC will require replacement.