car stopped running due to the fuel pump not working. changed fuel pump with a used fuel pump from a 1989 Corsica after about a months time of the car sitting. started car and it has a back fire coming out of the egr and the exit end of the catalytic converter but the back fire is not consistent. when gas pedal is held slightly down car will run but will not hold idle until warmed up and even then it wants to quit. car is also hard to start. checked plugs, wires, air intake and there is no check engine light. did not mess with anything else other than changed a heater core hose. please help in this matter It will be greatly appreciated. thank you for your time and effort in this. STEVE