Hi, I also had this exact same problem for 4 months. I have a 24-Valve 300E 1991. After many trips to the Garage, my mechanic changed the Distributor cap AND the Rotor Button that sits behind it. The rotor showed signs of corrosion and arcing that caused the rough idling and stalling intermittently. No problems now for the last 2000K's. If that doesn't fix it, you would need a very tall cliff!