5.8L high idle problem, 92 F-150
 

On the way to work this morning, I noticed the truck was idling fast when I pulled up to a stop sign. Truck was warmed up, approximately 7 miles at this point. I don't have a tach, but the seat of the pants feeling was that the rpms were higher than normal. The truck shifted hard between 1st and 2nd several times and hard between 2nd and third once, almost as if I had a shift kit in the tranny. It is stock E4OD. The shifting problem has occured intermittantly over the past year.

Anyway, the high idle was present at the next stop sign, and definately noticable when I pulled into the parking lot and shifted into reverse. RPMs jumped when it dropped into neutral between drive and reverse, then again when it went into park.

I searched the forums and found the most common problems to be vacuum leaks from broken lines or manifold gasket or else a bad IAC.

I went out and started the truck about 2 hours later. Checked under the hood to listen for vacuum leaks and checked the most visible lines for breaks. No obvious hissing. This time, the truck went through the normal idle procedure and idled down to normal rpms after a minute or two. For now, I would rule out a vacuum leak, since that would cause the idle to stay high consistantly. I'll pull codes tonight if I get a chance, although the check engine light is not on.

Any similar experiences, thoughts, or wild-a** guesses on this one. I'll keep an eye, ear, feel on it on the way home tonight to see if the problem re-occurs. Thanks for any comments, many of you have helped in the past.

hey i know its a little... alot late. but i was just wondering if you ever found any answers? my 89 5.8l f250 with a standard 5 speed tranny seams to be doing about the same thing, i can give the truck a quick hard rev and the idle will drop back down like something in the throttle assembly is hanging up but there is nothing obvious that is hanging. Could the truck be running lean? most of my smog equipment has been removed