Aaron's post parallels my experience with my pinging and vibrating 240D at low RPM, but I don't think my engine was missing. I added a bottle of the Red Line catylist (bought from this site) and no kidding, she calmed down by the end of the tank of fuel. Started to vibrate again within a thousand miles, but that proved to be a bad motor mount--maybe caused by all that vibration before Red Line?

Hope your problem is so simple!