2000 Malibu stalls more often recently then before. Thought it had to do with theft module... but theft light does NOT blink. Auto's previous owner had ignition changed... auto has two(2) keys for operation... one for ignition; one for opening doors. Auto runs well when running, but... When auto stalls; and key is turned to start... sometimes auto almost starts with RPMs only around 200-350. This "stuttering" may get better and then auto starts... or stall out . Will sheck tomorrow night for any and all help... thanks. Week

You may be looking at the early stages of fuel pump failure. If you wait (for the pump to cool off slightly) and attempt to start the car, you may better luck. If so, get estimates from more than one shop.
Let us know.

Check the fuel presssure. The fuel rail needs to be fully pressurized for the engine to start. Try turning the ignition switch to ON, waiting until the fuel pump stops running. Then, turn the ignition switch OFF. Repeat this process two more times. On the final attempt, turn the ignition switch to START. Other possibilities are the Idle Air Control Valve is bad or that the Engine Temperature Coolant Sensor is failing.