I spent this past friday going through and getting my 92 F150 back up in running condition. It's a 92 F150 XLT, 5spd, 4.9ci and it's been sitting for nearly a year with a few problems I just haven't taken care of. I hit the autoparts store and replace the battery, alternator, cap, rotor, plugs, plug wires, and the upper heater core hose. Get everything new put on and it starts up beautifully except that it's idling between 2k - 2,300k rpms and the tach won't drop below that unless I turn the truck off. Any ideas as to what I should look at with a high idle like that?

 

Stuck IAC? Major vacuum leak?

 

At warm idle, if you disconnect the IAC, does the Idle crash? if not, the IAC is pooched.

 

Well I took a long look at my truck with a buddy that's a mechanic and what we thought was a high idle has actually turned out to be my tach that's not totally working. Reason I say that is because it won't drop below 2K rpms but i'll pick right up from 2k+ when driving. Looks like I'll be pulling the gauge cluster soon.