Join Date: May 2009
Location: Bonney Lake, WA
Re: 92 f150 5.8 very fast idle 2500 rpm
Have you tried to run a diagnostic check on the ecu? If so, what kind of codes is it spitting out? If there are any codes present, that would help in diagnosing your problem.
This may not be your problem, but I had a '87 Ranger that did pretty much the same thing. I would come to a stop and the motor would stay at about 2000 rpm for a minute or so and then come back down to normal. Took a long time to figure out that problem, but it ended up being a faulty MAP sensor. The problem was that it wasn't bad enough to throw any codes. It was telling my ecu that I was at about 12,000 feet in elevation when I was in fact at about 100 feet above sea level.
1964 Galaxie 500XL, 352cid, Cruise-o-matic, 9in rear, white w/white interior, all original american iron as it came from the factory.
1992 F150, 5.0L, E4OD, 8.8in rear