Do yourself a favor and stay away from dealerships. Lots of good independent shops out there. As far as Mercedes buying your car back I think thats pretty much out of the question for a 7 year old car. And to qualify as a lemon it would have to have had the same problem at least 3 or 4 times.
I say find a competent indy mechanic and see what the issue with your car is and decide if its worth keeping. Sounds like you have an electronic issue with the throttle though.
I say find a competent indy mechanic and see what the issue with your car is and decide if its worth keeping. Sounds like you have an electronic issue with the throttle though.