Hello!

My 1990 F-150 run erratically when is hot. the engine run up and down. Hayne's manual said vacuum problem. Does anyone can help me ?

Thanks

Renoracing

 

make sure vacume lines are all there and check for splits. also take off the idle air bypass valve. its on the throttle body. pull it off clean it out with carb and choke cleaner. or if you have the $50 (i think thats what i payed for mine) go out and get a new one. does it seem like its not getting fuel? my 96 5.0 would act weird when it got warmed up. like it would get enough fuel then sometimes it would just bog down. turned out to be my fuel pressure regulator. somethin to look at. and how hot are we talking? over heat hot or just warmed up to about r of normal?

 

Thanks a lot,

I'm talking about warm up. Temp never be up to half gauge.

I think i hear some vaccum leaking but not sure from where it comes

-1 Will check idle air bypass valve
-2 will check fuel pressure regulator, but never do this.

Mine do exactly as your 5.0, would bog down and speed up but sometimes run erratically like past weekend ???