'89 grand prix with engine problems...help?

ok so heres the deal. i got this grand prix, and its giving me some major trouble. it likes to die for no reason if i take my foot off the gas pedal, so even when im at a red light, if i dont have both my brake and gas pedal pressed a bit, it will die. it doesnt like to sit at lights either. the engine will rev and all kinds of stuff...

so i brought this issue up with a mechanic, and he told me that it was the fuel pump. so i went and got a new one. it still died for no reason. i took it back to him and he said " oh well, the computer inside re-programmed itself since u had been pressing the gas while u were stationary, give it a week to get back to normal " that sounded all good and fine, but i cant just let it randomly die while im on the street. and sometimes it wont start again for a good 20 minutes. ive basically heard it all from oxygen indicators to ignition indicators to this fuel pump thing, and i know nothing about cars.

so can anyone tell me whats REALLY wrong with it?

thanks for any feedback

-extremely confused

Hey There,

Well, you say you have replaced the fuel pump and apparently it (engine) runs when the gas pedal is depressed. So, this sounds like a fuel management problem.
The basic approach for a car this old---my thought---is :

1) Is the fuel filter in good shaoe--when was it changed?
2) Could your fuel injectors be dirty? Or..do you have fuel injection?

There are other engine possibilities but these above could be overlooked. If you haven't addressed these--consider them. Be warned that putting fuel cleaner in a tank could be disastrous to a fuel pump. Careful on that idea.

John R