Pontiac Problems? Ask a Mechanic for Answers ASAP
Good morning, sounds to me like you have the famous clogged catalytic converter. They get plugged up over time from getting hot this causes the exhaust to backpressure into the engine until it dies.
You can pull out the front oxygen sensor to verify my diagnosis. If it starts or runs better with the plug out of the exhaust (other than the loud exhaust leak of course) replace the cat and your problem is solved. Thanks and have a great 4th.