After installing a new plenum intake gasket on my 97 conocrde 3.5..it did make the check engine lite go out.....I had also reset timing since i fixed a water leak...problem now...when car is started cold idle will be around 1000--still high--but as car warms up it jumps to 1500,then to 2100...I have double checked every vacuum port connection....Only thing I didnt do on the plenum gasket was use silicone type sealer--i installed it dry after both surfaces were completely cleaned off...

I wonder if I am leaking at intake...but then the check engine lite should have stayed on......

anyone have similar problem and what fixed it? thanks...Jeff

 

Browse around the forum and you will find a few threads discussing high idle speeds and the causes. It's almost invariably a vacuum leak. As far as the engine is concerned, it's the functional equivalent of an open throttle. One way to find a leak is with a tube held close to your ear. Probe around the intake manifold with the other end until you hear the ocean.

 

High idle in my 3.5 was caused by bad silicone seals on the egr tubes that run to the upper plenum. put them on the tubes first then set the upper plenum on them.