Help! Taken car to 2002 Mercedes C 240 to repair 3 times in past 5 months for engine light that comes on while driving and then car de- accelerates slowly and then have to pull over as the engine stops. By time get it towed to repair shop,light is off and no codes come up when it is put through computer. Always happens when it is hot and being driven on freeway, first fast and then stop and go traffic. shop can't make it replicate symptoms even when taking it out for long drives. Anyone ever heard of this? Could a defective key have anything to do with it? Now they are saying the key is defective and won't start car.