I have a very annoying high idle condition after warm up. During cold start it idles at about 1500rpm (dash tach) then will idle about 1000 to 1100rpm under warmed-up conditions. The temp gauge never gets above the "n" in normal so that is what I call warmed up.

The thing that really drives me nuts is when I shift (5 speed) the engine races up to a higher rpm or just doesn't settle back down very quick so I have to ride the clutch a little to get the engine speed down. It is really annoying and I am sure it is ruining what little gas mileage I get.

Can anyone help? My Haynes manual doesn't help at all. Here are other details:
302 V8 rebuilt 10,000 miles ago.
new filters, new fluids, new three-level rad, AC, 5-speed, 4x4, 7000 on clutch, 118,000 on truck.

Thanks,
Randy

 

If your truck is only getting to the n on normal your truck definately isnt running hot enough.
It should be runing somewhere between the O through the M. This is probably a mojority of the problem the computer senses the engine is cold and is running it rich all of the time. This is bad for all your components.
Change the thermostat it should have a 195.
good luck

 

Change the gasket between the plenum and the intake. my 92 was doing the same thing and this fixed it. As well as restored power. I found mine by spraying carb cleaner around the intake while it is running. if it is leaking in will smooth out when you spray it

 

Randy ,
When was the last time the throttle body , Idle Air Bypass Valve was cleaned ? Im sure if you look thru the posts here , your problem / condition is often caused by carbon buildup on the previous mentioned parts . Start with that , its the simplest to resolve , let us know if the problem persists .
Paul

 

It sounds like you have a vaccum leak somewhere

 

I had the same problem on my 90 302. I checked air bypass valve. throttle position sensor, all vacuum connections, MAP sensor, etc. Turned out it was the gasket between the intake runners and the plenum. That solved it.

 

shadetree wrench,
What do you mean by plenum? Are you referring to the lower intake manifold or the Throttle Body? I've been having the same problem as a lot of others have. I've also changed parts unneccessarily and scrubed the TB and IAC with no success. I did the ole (high tech) carb cleaner spray check and found a leak between the upper and lower intake manifolds; it is leaking at the front of the manifold assembly. When I do replace the gasket, I'll probably go ahead and scrub out the upper manifold before bolting it all back together.

 

I fixed this problem a while ago. To do it I did two things: I replaced the gasket that connects the bypass valve after cleaning it and that helped some. But resetting the computer finished the job (I removed the Neg battery cable for 10 minutes).

It was actually kind of a fluke. I couldn't figure out what was wrong and then my starter died on me. In the process of replacing the starter I had to disconnect the battery and reset the computer. Started her back up and she idled perfectly, no revving up when shifting or anything like that. I even changed the thermostadt because of the temp only going to "n" and found out that the temp sensor is sending the right voltage that corresponds to "m" in the gauge, the gauge is just shot. I am installing an aftermarket gauge set.

Only a few dozen more repair projects and the truck will be good to go again.

Later.
Randy