QuestionHi there, I have a 1997 pontiac grand prix gt, 3800 series II engine
Car has around 170k.
Idle is acting funny at times.
Seems to idle smooth, the needle is slightly unsteady, and sometimes its an obvious surge.
The main thing is sometimes after driving when its put in park it revs really high, 2500 or so, if i tap the gas it just bumps it up.
Another time it was stuck around 1500 I...
-checked throttle plate, was not stuck
-unplugged the tps, no change
-cleaned the IAC valve, no changed
- cleaned throttle body, no change
- Cleaned MAF, no change
Now, I am not sure if it was a coincidence or not, but there is a little plug in the air intake tube, Air temp sensor i think I unplugged that when it was stuck at 1500 rpms and it went right down. But I dont know if that can cause that, or if the car was just being sporadic and it was a coincidence, because this isnt and everyday thing, but often enough.
Do you have any ideas to shed some light on this? Thank you
AnswerHi Kolby:
Is thsi a supercharged 3800 engine or just the basic engine? you said it's a GT so I'm thinking super charged?? If so there is a vacuum leak in one of two places. the gasket between the super charger and intake manifold is sucks in near the front of the engine or the vacuum line that runs to the map/boost sensors is leaking. that line is under supercharger nose and there is a "T" in the line where it attaches to the engine. the line splits there and cuases vacuum leak. If this is a plain 3800 non super charged check on the back side of the engine where the vacuum hose goes to the brake booster. ther is a vacuum line right there that breaks on ome applications and on some there is a vacuum tap there that had a cap on it possably the cap split and fell off and it's sucking air there. The reason for the incresed idle is the engine is ingestion un metered air into the intake. If extra air enters the engine that the MAF doesn't see the engine computer adds more fuel so the idle speed increases. esentially with a vacuum leak it's like you have your foot on the gas to allow more air in but you don'r the vacuum leak is cuaing the same issue. good luck :-)
