Chances are the fuel pressure is leaking down when the engine is off. The check valve in the fuel pump can leak along with the fuel pressure regulator, but the most common cause is a leaking injector. GM has had trouble with injectors that were not flow-matched on the assembly line and they can cause minor running problems and a recurring Check Engine light with a diagnostic fault code for "running lean too long" or a cylinder misfire that you may not even feel. THAT is the time to replace all the injectors with a set of rebuilt and flow-matched injectors. Until then if there's no other running problem you will probably want to ignore it. The rough running at start-up is likely due to one cylinder being flooded with gas from the leaking injector. (It's not very much gas; perhaps a tablespoon). The engine will run a few seconds on what dribbled into the engine while it was sitting, then it stalls because the proper pressure hasn't built up yet. You MIGHT avoid having to start it twice by turning the ignition switch on, waiting a few seconds for the pump to cycle and turn off, turning the ignition switch back off, waiting a few seconds, THEN turn it on again and start the engine. Each time you turn it on the pump will run for about one second and start to build pressure. That procedure isn't fixing anything; it's just overcoming the symptom.
Monday, April 1st, 2013 AT 11:10 PM