My E39 528i 5-spd has just over 50K on it. Always serviced by BMW dealerships, by the book. Ran great until yesterday. Suddenly, the CHECK ENGINE light comes on and the car starts riding rough, especially at low speeds.

I had the exact thing happen to my 97 540i today. It ran rough and would stall out at low speed. I smelled a sulpher like smell coming from the engine. After shutting it down, it started up and ran fine and the check engine light went out. I plan on getting it checked out tomorrow.

I took it to the dealership immediately. Three techs spent an hour trying to figure out the problem. They put in new plugs and a new coil with no success. Finally, they did a compression test and found cylinder 3 at only 30 lbs. All the rest were normal! Initially, the service rep mentioned bent valves due to overrev on downshift!? Then he said it could be just about anything. So, they plan to start by tearing the head off on Monday!

Has anyone experienced anything like this with their 528 E39? I really don't want to have the head taken off if it could be software causing this. And, why the heck would only one cylinder be affected and the other 5 are just fine? Even the service rep later discounted the bent valve theory because more than one cylinder should be affected by that scenario. He said the techs can hardly wait for Monday to get that head off and see what's going on - YIKES! I don't want my E39 to be a guinea pig. HELP!