My 2010 GT does the same thing. Generally it is after the car has warmed up some-then have to restart. This is a safety issue if you try to drive right off. I was going to ask the dealer I am having it service at to fix this ( United BMW of Roswell ). There is an SIB to address this issue but from what I understand the idle fluctuation does not throw a code. I will be very disappointed if they don't fix this.
Which dealer said they could not fix this?