Engine hesitates

1992 subaru loyale with 134232 miles. I have recently inherited this car. The old owner recently had timing belt and water pump replaced, in addition to replacing the plugs, wires, air filter, rotor, distributor, and he told me that the injecters have just been cleaned. Nothing done to fuel filter or fuel pump. Car appearred to be running fine until the recent cold weather, I have had the car for about 4 days. When starting the car, the car will quickly stall and then after two or three tries it will keep running. The car hesitates and back fires before stalling out if I press on gas pedal sharply. If I ease on the gas pedal it will slightly hesitate but stay running. This problem seems to stop once car is fully warmed up or if I am driving at a steady speed. Do you have any suggestions