88' 300E - 154,600 mi, clean, perfect - except that when engine is hot or cold, in warm or cold weather, almost every time the car is started, car starts immediately upon cranking, then stumbles - feels and sounds like you can count the detonations for about 3-6 seconds, then resumes normal idle - otherwise, perfect engine operation, power, response and gas mileage - no missing or hesitation - comments as to possible causes and how to repair will be appreciated