hi i have a vl commodore that was oridginaly a 6 cylinder and has been converted to 304 5.0 injected , car was running great when i first brought it ,since then when motor gets up to running temp , then the car starts missing and running on 6 or 7 cylinders then at idle will cut out if im sitting stationary in gear, up and until car is at running temprature , runs prefect if any1 knows whats going could you help me.