Intermittent Engine Shudder While Driving
This bulletin involves replacing the engine cylinder heads.
A small number of customers may experience a slight engine shudder while driving. They
may state that the condition feels and sounds like driving over rumble strips. It may also be
perceived as an internal transmission issue or engine misfire. No Diagnostic Trouble
Codes (DTCs) will set as a result of this condition.
DISCUSSION:
The root cause of the engine shudder has been found to be due to excess carbon build-up
on the exhaust valve stems and will typically happen on vehicles driven mostly in light load
conditions. As a result, new cylinder heads have been released that are equipped with
newly designed valve stem seals. These newly designed seals are designed to help
prevent excessive carbon from building up on the valve stems.
Although it may be hard to reproduce, engine shudder resulting from these excess carbon
deposits, will typically only happen under the following driving conditions.
? Steady speeds between 50 and 70 mph (80 and 113 kph).
? Engine speed between 1600 - 2000 RPM.
? Present during engine warm up to operating temperature after a cold soak.
? Only present for a few seconds at a time and often during a 6-7 upshift.
? Light load acceleration or while driving up a slight grade.
? Symptom will go away either by aggressively applying the accelerator pedal or going
into a zero throttle deceleration.
