i am having the same problem on my car. When I took it to the dealer they said it was the coil. I have 80000 miles on it now. Anyway it happens mostly when at a stop light. I know exactly what you are feeling. I thought it was gas because once i filled up with some Exxon (using shell always but needed gas and had to stop at the Exxon) and it got worse. I also had washed it and someone said it could be the moisture. let me know what you figure out.
Oh and they wanted 850 to change the coils and plugs.
07 - 328i Coupe