Rough Running On Initial Cold Start - Under Investigation - keywords all cylinders DTC engine foul fouled fouling hesitate idle intermittent light MIL misfire miss no on plug plugs random run SES

This PI was superseded to remove the reference that advised to expect a correction during the 4th Quarter of 2006. Please discard PIP3956.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

On rare occasions, a brief rough running concern may be experienced for less than 1 minute after cold starting the engine. Once the concern disappears after start up, it will not occur again until the vehicle sits with the engine off for at least 4 hours or more. Typically, no DTCs will be stored but a P0300 and/or P1400 may set if the concern lasts long enough due to random misfires on all cylinders. Additionally, early reports indicate that this concern is more likely to occur if the customer uses mid-grade or premium gasoline since they are less volatile than regular unleaded gasoline.

If the SI diagnostics do not isolate a cause for this concern, perform the following suggestions as necessary:

1. Carefully inspect the air intake system for any evidence of air flow restrictions or air leaks that would allow unmetered air to enter the engine.
2. Replace the air filter element.
3. Advise the customer to use only regular grade (typically 87 octane) unleaded gasoline from a high volume filling station and evaluate the concern again in 1,000 miles.
4. If this does not correct the concern, no additional repairs should be performed because this concern is currently under investigation. In the meantime, this concern may be improved if the customer presses the accelerator pedal slightly upon cold start.

Once a correction is developed, this PI will be placed in SI with additional details, and a proactive communication will be sent to all dealers that have active TAC cases on this concern.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.