1) go to AUTOZONE if you have one of the stores near you, and have them conect up to your OBD plug and check for any codes. If your AMM-air mass sensor is starting to go it won't throw a check engine light for a while.

2) I didn't see you mention a new air filter, and don't know your mileage to see if new spark plugs might be a worthwhile but long-shot kind of throw parts at the problem to see what happens.

3) haynes does have a non-supercharger euro-UK version manual for your car and Mercedes does have manuals on CD's - but I'm not familiar with these CD's.

4) do a google search on STAR TUNED MAGAZINE & www.mbwholesaleparts.com