setting idle speed on F150 302 ci 1992 129000miles

John, the idle in your truck is controlled by the computer. First thing I want you to do is remove the intake tubes at the throttle body, have someone hold th ethrottle wide open (engine off) and clean out around where the butterfly's are when they are closed with a little carb spray and a rag. Reversion builds up in there and the correct amount of air cant get by. Put the idle screw back where it was when you started. Truck may run a little rough from carb spray but it will clean up.If that doesnt fix it, then you might need a new Idle Air Control Valve. It is what the computer uses to control idle speed. Good luck.... get back to me