Leak in intake manifold or deteriorated throttle body gasket;
Loose or missing throttle body spring;
Defective idle air bypass valve;
Bad throttle position sensor;
Bad EGR valve or EGR position sensor;
Evil aliens.
If there is, or has recently been, a CHECK ENGINE light showing, have the stored codes read out. They may reveal the culprit or, at least, indicate where to begin looking.
when i buy a "new" vehicle i go to autozone or pepboys and buy a repair manual for that car's year,make,model. it has saved me alot of time and money spending $20 for a book. they have pics and step by step instructions and also a trouble shooting section where you can identify solution for you cars issues.
Pretty sure your car has struts on the rear and the shock function is part of the strut. Replacing struts is more difficult than replacing shocks and they should be replaced in pairs.
How to replace crankshaft sensor on grand prix gtp
The above link is for a video how to replace the crankshaft sensor on a different vehicle than your ,but the procedure is the same for your vehicle. The Harmonic Balancer needs to be removed to access the sensor, which is the most difficult part of the job.
There many videos on how to remove the harmonic balancer, and how to replace the crankshaft sensor on the GM 3.8 engine. Do a search on the web ' how to remove the harmonic balancer GM 3.8 engine.'
Hope this helps. Good Luck!
if your refering to the light on the odometer and its dark there is a little resister on the back of the cluster that you cannot fix yourself unless your an electronic oriented person. this happened to me. I went on ebay and bought another one and it worked about 2 years and not its the same thing, black with no light. I read some where these are warranteed for life by buick and they have to replace them but that was around 8 years ago and not sure if it still applys.
I would look at the security system if not working correctly car will shut down and will not start cuts off gas supply and cranking ability. Hope I was a help Joe