I recently purchased a 94 500E that I've been working on slowly. Car had a heavy misfire at idle. A quick inspection of the vehicle and I noticed 4 spark plug wires were not seated fully on the spark plugs, fixed that and the car ran slightly better but still unacceptable. I then noticed 2 of the injector connectors were not plugged in, plugged those in and the car ran slightly better, but still not acceptable. Pulled the plugs and saw they were not the correct type, changed those and the car ran near perfect... until the engine warmed up and then I would get the heavy misfire again... pulled the caps and rotors and then I found this on the drivers side:
Car is still on its original set of wires, so that needs to be changed next but as of right now, the car runs near flawlessly. There is a very slight miss/stumble every now and again and you have to be paying attention to notice it. Wires have to be changed and I need to check the insulators behind the rotors.
Car does need an upper harness.