We had the "Check Engine" light come on last month on our 96' C280 with 79k on it. We took it in to a Mercedes independent in our area and had it looked at. Well it turned out to be an Oxygen Sensor, the mechanic showed us the junction between the wiring and the sensor body and there appeared to be a tear between the protective layer of material, so we had it replaced. He also had his exhaust measuring equipment hooked up and operating.
The problem is, about 20 miles after the replacement, after shutting down the engine, you get a strong sulfer-ish smell from the exhaust pipe. Not sure if this is related, but the gas mileage has never seemed great in this car with mostly highway cruising(haven't calculated mileage yet, as the car is not driven often).
Anybody have any suggestions and thoughts?