Bought a 2006 cobalt ss lsj with a blown head gasket replaced it and had to time it. It will start when I push the pedal and it will stay running as long as I am on the gas, but as soon as I let off the gas the idle bounces up and down and the car dies, I’ve torn it apart and put it back together over and over, checked the cam sensor, and still won’t act right... any thoughts?

 

Sounds like an injector problem, sensor problem, or a tune problem.