1988 Chevy Celebrity difficulty starting/stalling

This car often has problems starting. If I hold down the gas a little it will not stall on start, or will actually start and run. Often when the car is running fine it will just stall, usually at speeds between 15-30 miles an hour. The ECM was recently replaced and it solved a lot of other problems the car had (non-functioning speedometer, check engine light) but the occasional stalling problem continues.