4/2011 build 2011 n55 335i xDrive with 50k on odometer and I've been experiencing same surging idle at low speeds particularly whiles turning the steering wheel when parking
My car has been doing this since 40k miles when I bought it.
I mentioned it to the bmw dealership while the car was still under warranty and they went thru everything and couldn't find an issue.
A tech said the surging was a normal N55 E90 thing that happens when steering at low speed.
Sometimes it is a soft surge other times the surge in rough and the car seems like it is lurching forward on its own
Seems like we all experiencing the same thing