Have Mercedes Questions? Ask a Mechanic for Answers ASAP
Hi, welcome to Just Answer. My name is***** sounds like you have developed an ignition misfire. If the car runs smoothly when you turn the motor off and back on again it indicates an intermittent misfire. If the car continues to run rough after cycling the key off and on it indicates a permanent misfire. Common cause of an intermittent misfire would be a restricted catalytic converter. Common causes of a permanent misfire would be a bad ignition coil or ignition wire or spark plug. There are quite a few other possibilities as well. You will need to get the car hooked up to a Mercedes diagnostic tester in order to read out the fault codes stored in the engine control module. The fault codes will point to the specific problem.
Let me know if you have any questions.