Low Idle and Searching/Bouncing Idle

[MikeyP]

My 1990 V10 does the same thing...

Fast idle at startup as expected til operating temp. Once the truck is at operating temp the idle drops and begins to lope/gallup with a good amount of vibration when stopped in gear. If I put it into gear (forward or reverse) before operating temp it slams into gear pretty hard. This also happens when driving cold and the tranny goes into second if accelerating.
My temp sensor is new, as well as EGR, all maintenance is pretty much up to date. TBI gaskets are new.
I was suspecting an intake manifold leak, but you pretty much ruled that out with your explanation.
A friend suggested that the cam lobes are worn (I have high mileage close to 200,00 also.)
Other than that It runs like a beast, great acceleration, flys on the highway with great MPG and will do well over 100 mph.
Let me know if you come up with anything, as this situation is driving me crazy as well.

Peace,
MP

 

[clay1937]

I'm really beginning to suspect a manifold vacuum leak that only exhibits itself when the engine is hot, and is very difficult to find.

I think I'm going to take it to a different local Chevy dealer for another shot at diagnosing it, and see if they can find a vacuum leak.

Thanks!

Clay

 

[MikeyP]

The intake would be better than the cam I guess.

make sure to post when you figure it out. Sounds like we both need a rebuild either way.

MP

 

[eagle mark]

I'm really beginning to suspect a manifold vacuum leak that only exhibits itself when the engine is hot, and is very difficult to find.

I think I'm going to take it to a different local Chevy dealer for another shot at diagnosing it, and see if they can find a vacuum leak.

Thanks!

Clay

Unfortunatly with the Chevy engine you could have an intake manifold vacuum leak that is inside the engine and undetectable.

Have you tried the starting fluid? If it's sprayed on a vacuum leak the engine idle will raise.