Hello everyone
I am new to this forum and to the Ford community. I have a 1991 F150 XLT Lariet with a 5.0 302 5 speed manual. The engine idles high at all times. When the eng is at running temp and I push in the clutch to up or down shift it climbs up to between 2200 and 2500 rpm. I just got the truck and can not find anything in the Haynes I bought. I am a decent mechanic so I understand the workings of an engine. Thanks in advance for any help I can get.

 

Check for any codes first.

Causes- Vacuum leak(s) at critical areas such as the intake manifold, PCV hose and the brake booster vacuum line. Check for proper operation and cleaning of the AIC system. Make sure there are no mechanical reasons for the throttle blades not closing completely. Those include a idle hard stop screw which was messed with or a binding throttle shaft within the throttle body. Lastly, a malfunctioning throttle position sensor can cause high, erratic idle speeds.

 

I’d also suggest checking for any vacuum leaks or issues with the throttle body. Give the throttle body a good clean. Any chance the idle control valve might be acting up? Also, double-check the coolant temperature sensor to make sure it's working right. If it's not working right, it might mess with the engine control module and mess up the idle.

 

Any links on here on how to check for proper operation of coolant temp sensor?

Thanks!