Ford Repair: F150 uncontrollable high idle, negative battery cable, throttle position sensor

Question
My 1989 2W/F150 5L/F.I. has extremely high idle (guessimate 2000 RPM). Computer checks (internal and external) do not show any fault other than high idle. The idle has crept over the last year from about 1500 RPM upto about 2000 RPM. I have run simple tests on IACV and Throttle Position sensor. They seem to be OK. My son has put it on the computer at his school and it did not show any thing.

Help!

Answer
Hello and thanks for the question...I'll try to help.
 WHat I would suggest you look for is a vac leak, external or internal in the engine. The external leaks are usually vac lines, or valves that are cracked. The internal leaks to check are the plenum gasket (the big silver thing that holds the throttle body), PCV valve, and EGR valve.
I would also suggest that you disconnect the negative battery cable and reset the idle strategy. Wait for 10-15 minutes before reconnecting it. Then dive the vehicle for 5-10 miles, going from 0-55 mph.
You might also want to clean out the throttle body with a mild cleaner on a rag.
Hope this helps,
Erik