you know, with these older cars, Mercedes used a vacuum system to run the power locks, shutoff system for the engine, cruise control and many other things. it isn't Mercedes fault, but its because the rubber is old, then dries out, and then loses its vacuum. now i tried using electric tape, and wrapping the connections on the vacuum lines, and it seemed to work. now this could work for others, but remember there are vacuum lines through out your cars. the one ting that it could be, but it rarely is, is the vacuum pump. it hardly is the cause of the problem, but it never hurts to have it checked out! good luck with your problems. and diesels idle rough naturally cuz its not ignition, and spark plugs to run the engine, its compression! and when the engine continues to run after shutting off, thats called dieseling. well good luck!