i have a 1990 f150 5.0, 5 speed.In between shifts the idle jumps to a higher RMP if i shut the truck off and restart it, it seems to be fine like some kind of sensor is being reset?? pleaseeee help its annoying!could it possibly be the IAC????

 

Wouldn't hurt to try cleaning the IAC.

I am assuming this is a manual transmission as it revs betwwen shifts. May not hurt to clean the throttle body out as well to make sure the butterfly is closing properly when you let off the gas to shift.