car starts but sputters and dies

It's probably the crankshaft position sensor. Mine went out a few months ago and I had the same symptoms. The sensor can be bought at any MB dealership at half the price of any auto parts store (I paid $95 at MB dealership, parts store asked 230-380). Shops will charge anywhere from 600-1300 to do it so I suggest doing it yourself. It only has one screw holding it in and one plug in it so it is easy to do your self once you get your hand crammed in between the firewall and the engine. It took me about 30 minutes just to get my hand in there but once I did it only took 3 minutes to pull out the old one and put in the new one.