Last week I replaced the IAC valve and TPS sensor with used ones to solve my high idle problem. Through these forums, I had narrowed it down to a problem relating to the throttle body. That solved the problem for a day then went back to the old high idle at 1500 rpm. Tonight, I took the truck to the ice rink down the highway at 55 mph speeds. It had no problems until I turned off the highway. There, the idle shot up to 2000 rpm. Even when in gear, I didn't need to use any gas because the truck maintained 2000 rpm. I was puzzled but got to the parking lot fine. I left about 3 hours later but the truck would not start. It was not too cold or raining out. The engine turned over but wouldn't start. After a jump start, I headed back to my dorm. Upon arriving, the truck started just fine in the parking lot at my dorm as if nothing was wrong (other than the high idle). I think it could be an ignition problem or vacuum issue. Ideas? I have almost no tools here so my self tests are limited. I was going to call a mechanic but I don't want to get stuck again.

 

Have you tried a spare map sensor?

 

There could be 1 problem or several. With Ford's OBDI, problems can occur like a stack of falling dominoes, with 1 good part showing failure, whereas its further up the stack.

A consistently high idle could be attributed to worn throttle body blades, worn Tb shaft, weak return springs for the Tb blades. Other possible causes; Failing or failed O2 sensor, bad signal from O2 sensor, stuck open PCV, EGR valve is stuck open, intake leak b/w plenum & lower intake, intake leak b/w lower intake & block, and any number or vacuum lines coming off the "T" from the plenum. As a member mentioned earlier could be the map sensor as well.

I would check to be sure plugs are fine noting condition of them and be sure they aren't plats and are gapped correctly. Also be sure the plug wires aren't damaged.

 

I'll check the wires and all the visible vacuum lines this morning. I have appt with the mechanic for Thursday as I am at college and away from my tools except for my basic wrenches and screwdrivers.

 

Have you tried the paperclip method to pull codes? Go to fordfuelinjection.com for the exact procedure.