Car runs and drives but will stall

I have an 89 chevy celebrity 2.8l MFI V6 If it idles in park too long or if you press the gas pedal the engine shuts off and if you try to crank it too many times it wont start until it has sat for a while. We have replaced the fuel pump, fuel strainer, fuel filter,one injector, intake plenum gasket, throttle body gasket, egr gasket, throttle position sensor, oxygen sensor, and crank shaft position sensor. The car also burns real rich when its running. No check engine light comes on either.