Please Help Me

My car cranks and runs great as long as you are in the gas or idling in neutral or park, but if you stop at a stop sign or at a light it dies like you just turned the key off I've taken it to several mechanics and they can't find the problem we've changed every part and checked every part we can think of distributer and distributer cap ignition coil idle censor checked the vacuum lines gave it a tune up the works please if you know what it might be or have any ideas let me know I'm desperate for help! It's a '91 Camaro V8 we have changed the fuel pump we have changed what seems like everything but it still dies so apparently we are missing something please i'll take any advice you have!