I have an 87 F150 with 302 and EFI. I have a problem with the idle. Sometimes it idles normally a little below 1000 RPM's but often after driving awhile it idles too high- up around 1500-2000 and sometimes I have an idle surge. if I turn the car off for awhile it idle normals normal again. I replaced the little cylindrical valve on the intake- idle control solenoid I believe- and it didn't help. Whay else to check? Could it be the O2 sensor?

 

You may want to plug all vaccum line going out of the intake manifold, check your problem is gone. Then start reattaching the lines to find your problem source, then troble shoot from there. good luck

 

read the OBD and see what comes out. yes vacum would be my first guess(you can use a can of carb cleaner or unlit propane and spray around all hoses and conections). then i would also check the power stearing pressure switch

 

I was just wandering if you found the problem because i have a 1991 with the 5.8l that does the same thing.

 

You might look at the base of the upper intake. The gaskets there has a tendency to get blown out. Get a flashlight and look under the umbrella of the intake. If you see any gasket material sticking out, then the gasket is blown.

 

I hace a 1991 Ford f250 4.9 l6 AMD seem to have the same problem I'm try to change the manifold gasket to see if that fix the problem