what cause the car to shake while at the red light
Sounds like the engine is misfiring. Is your check engine light or service engine soon light on/flashing? If your Grand Prix has over 100,000 miles on it, your due for a tune up. HTH. -Jim
Engine shaking = tune-up time. Air filter, fuel filter, plugs. Get the injectors cleaned. Inspect those 10 year old ignition wires for burn marks, missing insulation.
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