My vehicle is a mercedes benz E220 CDI. When I spark the engine, it shakes and vibrates noisily for about 4-5 minutes before it runs smoothly. I have recently changed the engine seats. Also, when driving in town, the engine cuts off by itself very often. I then have to wait for about 30 seconds before starting the engine again. It responds only to cut off again. What may be the cause of this problem and how do I go about solving it?