The temp sensor on the rear of the head could cause this as well as the dist. cap and or the plug wire ends. The ends and the cap/rotor can be purchased through the partshop!
If you can't solve it you should consider a tech/shop in your area.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM