ECC problem

I have a 97 Cavalier. I was having problems with a rough idle on the car. Took it to the shop and was told it needed a new fuel injector. Had the fuel injector replaced, still the same problem. Took it back to the shop and they said they couldn't find anything wrong. Took it to another shop they said I had a blown head gasket. Now, I have had the head gasket replaced, new valves while the gasket was being replaced. New plugs, new wires, new MAP sensor, cleaned IAC sensor..... still the same problem that I started with. The mechanic said that I needed to replace the ECC. He got an ECC from another Cavalier, now the motor runs smooth, just like it was new (as long as the transmission is in park, reverse, or neutral) as soon as you drop to drive the car cuts off..... Any suggestions of what could be wrong now or how to fix this problem? (I am getting frustrated with throwing parts and time into this and still no fix):frown:

I know this night seem minor, but have you replaced the fuel filter recently?

I had a very similar problem and that was the trick.