Your question is fairly vague, but I'll try to guess what you mean. For that model of BMW, I have seen a lot of oil leaks associated with the valve cover gasket. The oil runs down over the exhaust manifolds and burns from the high heat. This might be the "smog smell" you are referring to. As far as the shut off at idle is concerned, I would check the throttle boot first. The boots have to flex a lot because they bring air from the air cleaner/mass air flow assembly to the throttle body on the intake manifold. The air cleaner is bolted to the body, and the engine sits on rubber mounts which allow it to move with respect to the body. That's what generates the flex. As the rubber boot gets older, it drys out and cracks which lets unmetered air into the engine. This causes the engine computer to incorrectly meter the gas and feed the engine an improper mixture. The effect is more pronounced at idle speeds which can cause the engine to die. At higher RPMs, the problem is less noticeable.
Let me know if that helps.
Dr. Loot's Assistant
Sunday, December 27th, 2009 AT 6:34 PM