Just to keep you posted on the MIL warning on my car. I finally had the glow plug control module replaced on Friday and problem solved
The engine is actually running smoother than before. The new control unit was ordered from Mercedes Benz because it was a lot cheaper there than at Chrysler. Still it cost me about 280 dollars. My mechanic tells me that this control unit is smaller than the original unit and that it is the 4th "generation" of these units. Mercedes has been having problems with these units for quite some time.