The correct Bosch plug for this car is an F8DC4. You list another plug with an "R" in the designator. I'm not 100% sure but I believe the "R" stands for resistor. If you have resistor plugs installed, they are most likely the cause of your problem.

J. M. van Swaay

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1994 E320 Wagon, 230,000 miles
1995 E320 Sedan, 106,000 miles
1994 E500 Sedan, 79,000 miles