I have a 2000 Grand Prix. The engine starts, but immediately stops. It will start and run if I press the gas pedal, but dies again when I let off the gas pedal. The problem has never been there before today.

I had a similar issue. It was simply a leak in the emmisions - Disconnected hose.

Your choke is stuck..Will it do that, when the car engine is warmed up? Wind it out in low gear, to blow some carbon out, mine did that when I did not drive it for three weeks, and my wife never goes over 50.When I punched it down, I looked in my rear view mirror, and could see all the clouds of smoke just pouring out..Good Luck..

I also have a supercharged G.P. 2000 it ran fine to the park I parked it then when i went to leave it would hardly start and the exhaust smelled like sulfer and it wont stay running i towed it home and changed the plugs then it started fine and ran fine for a couple of minutes then started doing it all over again if you figure your problem out or if any one can help that would be great

You can try taking the fuel pump resistor out located behind the washer fluid tank and mounted to the inner fender well. It is kind of a pain to get to, but if you remove the resistor and inspect the wires you might find a break in the the wiring. If you see any breaks go ahead and repair them and reinstall the resistor. The resistor looks like a ceramic horse shoe with two wires coming out of the end. If you have a mulimeter you can ohm the resistor to see if it has continuity, if not replace it. Happy motoring!

if your gp is supercharged it is the fuel pump reieisot only available from dealership

The most likely problem is that you have a stuck/failed Idle Air Controller. This is a device that (as its name implies...;-D...) controls the air flow into the engine when you have your foot off of the accelerator pedal (which closes the throttle plate and chokes off air to the engine).

By pressing on the accelerator pedal, you are allowing some air into the engine which enables it to run. Once you take your foot off, the throttle closes and the engine starves for air.

Good luck