I posted a message a while back and got some good advise, thanks. But my 1990 F150 5L still idles hi after cleaning the throttle bores and now a new idle by pass valve. Even had a Snap on code reader on and could pull no fault codes from the computer. Does anyone know if a upper intake manifold gasket leak would cause this problem.
A propane bottle with long hose on passed around the outside of the manifold raised the idle level only so slightly but I couldnt get under the inside of the manifold that well.

 

i had the same problem with my 91 5.0 and itwas the gasket,replaced the gasket and everything was fine,good luck

 

the upper intake manifold gasket is very likely to be the source of the high idle. It is fairly common.