Ok, I am a Mercedes Benz Mechanic and my 420sel is only my winter car, But the problem i have is it idles rough and I can not figure out what is going on. I have put on distributor cap, rotor, wires, plugs, different ignition control unit, coil, almost everything for the ignition system, I have also run 93 octane with bottle upon bottle of injector cleaner, tapped on the injectors and everything. But still the car idles rough at idle. Do i have to tare the motor down and have the valves reseated? Has anyone else had this problem and was able to fix it with out engine work?