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????

 

take off and clean iac then try it. Have you checked for codes at when engine is warm?

 

check your throttle body gasket. i had my 4.9l 5spd do the same thing. took it in to get something else fixed and the mechanic had found that the throttle body gasket was bad and getting sucked into the engine... to check it take some carb. ore break cleaner and spray it around the gasket. if truck changes in idle or dies this is the problem.

 

well ive been going through and replacing anything and everything all the sensors do you think that would be the problem though??i would just replace it

 

and yes i have had it on a scanner i have no codes my check enigine light isnt on

 

its a brand new gasket.

 

I changed the Idle air control valve..and the Throttle position sensor..Runs like a top
75.00 IAC..10 mins
33.00 TPS...20 mins