I don't know the specifics of your car, but i had a problem similar in my 240 dl. It ended up being the mass air sensor, you might think of checking that, Also check the oxygen sensor. The other thing that it might be, and i don't know if you've checked this, is your injectors. You've checked lots of things behind that, but nothing in the engine compartment. This is just based on common knowledge of cars, so none might apply, just some suggestions.........