Wat does it mean when my car is overheating and making this rattling noise and worst when I hit the gas....
Severe engine damage will result if you continue to operate that way.
Your car has a feature that will try to prevent engine damage when the computer senses an overheating condition. The computer will begin firing alternate cylinders and use the non firing cylinders to aid in cooling. Kind of like an air cooled engine. When this happens the engine will run poorly but is designed to get you off the road. The overheating condition needs to be addressed. This feature is not designed to be used all the time! HTH. -Jim
A plugged catalytic converter springs to mind although it could be a number of other things too.
Looking for a Used Grand Prix in your area?
CarGurus has 1,755 nationwide Grand Prix listings starting at $800.
Search Pontiac Grand Prix Questions
Pontiac Grand Prix Experts
Related Models For Sale
Used Cars For Sale