Jim Grant's Tech Tips
'95 Pontiac 3.4L, High Rev Engine
The 3.4L engine in my 95 Pontiac revs to 4k to 1k when
its cold. I spent $800 for a repair shop to solve the problem. They
did vac checks, tune-up and still the problem is there. However, if I
let the car sit for a day and then start it, it runs perfect!......Dale
Your description is much like that of a failing intake manifold gasket.
The intake manifold gasket on your engine design is a two part gasket.
The problem area of the gasket is with a flexible silicone seal. With
age the seal is not so flexible in cold weather, resulting in a failure
that creates a high and uncontrollable idle speed. The problem in diagnosing
this problem is that the engine has to run only a short time before enough
heat is created that the not so flexible seal becomes flexible. Whats
really neat about the problem is if the vehicle is left running the problem
will last longer than if the engine is run for a short time and shut off.
The momentary shutdown allows enough heat to reach the seal. Once flexible,
the problems gone.