Bo,
FWIW, be advised that an O2 sensor can go pretty bad before it throws a code. In my 300TE, my mileage goes to pot long before it ingnites the "check engine" light; in my 500E, the car ran like crapola at 1/2 to 3/4 throttle until I replaced the O2 sensor. It appears that the MBZ computers are fairly tolerant of an underperforming O2 sensor; in this case it's gotta be time
