I have a Cat GP40K with a Vortec V6 engine in it that would not idle. We replaced throttle body, Mass air flow sensor and the accelerator pedal sensor. The engine will now start for a few seconds, but hunts for idle, then dies out. We can remove the fuel supply hose at the mixer and hold it a away from the fitting about 1/4" and it will run. It dies out as soon as we intsall it. There are no codes.