Thanks to all that have replied! I changed the plugs last night, and as I do once a month, I checked the air pressure in the tires(set to factory #). If the mileage does not improve after the plug change, I will try the O2 sensor. I have the service CD, does it describe the best method for checking the o2 sensor? I really enjoy the car so far, albeit I have already fixed numerous small things, I am certainly sold on the Mercedes brand now, If a 16 year old "baby" benz drive as well as this, then I can't wait until it is time to buy a new one for the wife next year. Nothing I have ever owned has felt so solid after 119,000 miles. Now I can see why people become "mercedes people". This car will be a dream to drive after all of the small "bugs" get worked out.