The most common cause of rough idle and running complaints on this engine is corroded distributor caps and rotor buttons. It seems the dealer was going for the quick easy fix, and was in too much of a hurry to get it out the door thus not seeing that the coil wire was not routed properly. If the caps were indeed corroded and green looking inside then they did need to be replaced and may have been part of your running problem but not the only cause. Other possible causes are a bad engine wiring harness,i.e. insulation cracking.I have also seen throttle actuators cause problems as well, the insulation cracks and causes shorts just like on the engine wiring harness.
I would suggest having your tech cut open the harness on the throttle body to inspect the wires inside. If the insulation is cracking then you are going to need a new throttle body.
The air mass sensors do cause running problems but dont usually cause a rough idle. Not knowing the service history of the car the problem could be as simple as a faulty spark plug or a faulty resisitor end on a spark plug wire.
Mercedes Benz Master Tech