I have had the same probs with my mb lately and know it's a vac leak but haven't been able to figure out exactly where. Looking through the records of the previous owner they had the same problem twice and both times it was a vac leak in one of the door locks. If you lock your doors before you shut down and it cuts off faster or at all then supposedly it's leaking from one of the door locks???? my 300 td won't shut down at all unless i lock the door a few minutes before shutting down.