Thread: 2000 Grand Prix GT Idle and Hesitation Issues

I had the same high pitched sound and it turned out to be the hose coming from the booster to the back of the UIM. The fitting on the UIM was leaking ever so slightly and throwing everything off. Replaced the tree fitting and orings on it and threw a light coat of gasket sealer around it before install and once it snapped into place solidly on the UIM the issue went away. Seemed to be worse due to the aftermarket UIM as I never had that issue on the OEM one.

Also, did you use a stock MAF or aftermarket? These cars are known to be picky with aftermarket stuff. I usually just grab one from a JY if need be. Plenty of cars came with the 3800 as long as you get the right part# which should be stamped on the top of it.

Another thought is to check the wiring harness to the MAF and TPS. They get cooked by engine heat over the years and get brittle.

Thanks for the reply. MAF sensor was a JY unit, and made no change when I switched it.
The issues were here before AND after I did the whole intake gasket job. I used metal felpro for the LIM gaskets, and a ATP brand UIM gasket kit with Upper Manifold. I'll check the tree out, maybe something is messed up with it. Wiring looks good, but I could trace it farther to make sure.