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Hi, sorry for the wait I was away this morning. If the car starts and runs fine now I suspect that you may have lost a little compression in one of the cylinders possibly due to a collapsed valve lifter. If this only happens when the car sits for days I would suggest an oil and filter change if it has not been done for awhile. Other possibilities are loss of fuel to the fuel injectors due to fuel draining back into the tank. A faulty spark plug or a fouled plug due to faulty valve seals could also cause the problem. You might also have a fault in the variable valve timing mechanism. The check engine light came on because it misfired and the light may turn off after you drive it awhile. I'd suggest getting the car connected to a Mercedes tester to read out the fault codes that were stored when this happened. The codes might help to narrow down the problem.
Let me know if you have any questions.