I had very similar symptoms with my 95 E320. After going through several sets of plugs, I went to the owners manual and got the correct plug number. Parts stores had a "replacement" plug, but it still ran like crap. I got the correst plugs from the dealer - a little more but worth it. At the same time I replaced the resistor ends on all six plug wires. I believe this was the offending part, as I have since had no other problems. It was also the path of least expense, considering I was looking at replacing mass airflow sensor, etc. I ordered them from Performance Motorcars for about $65. A quick fix. I suggest you get the right plugs and replace the resistor ends. Bet it works.