I had a similar problem with my '98 E320. Search using my login name to find the thread about my stalling problem. It ended up being the knock sensor. I saw no DTCs with a simple scanner, but my mechanic caught it with his scanner after several visits. He also contacted a MB factory rep. about the problem. The MB rep. said that they are seeing more knock sensors fail on the older w210s.
I'm no mechanic, so I imagine I'm only confusing the issue for you.