Sorry, i just receive a call from the dealer because of the same problem that you're having. My pastor car is having the same problem. The car started moving very slow and the mileage is @ 98,000. I was told that the catalytic converter is bad. The quote i got is $2000 just for the CC not including everything else that i need to do on the car. The total cost to bring the car back to life is $3900. The car is also a 1998 ML320..
Tony