[Frozen Fractals]

So...this morning I woke up for work and as I was backing the car out of my garage (cold start, about 71F or 22C) it started surging a little. I drive a recently acquired 2006 BMW E90 330i with 110K on the clock. This issue has never occurred before in the three weeks I've had the car in my possession. I was just wondering what could be causing this and how to alleviate the issue (if it isn't a one off thing). Any help or insight is much appreciated!

More details:

- Opened garage door
- Started car with foot on brake and within a second or two, put it in reverse
- Let foot off of brake and car started backing up slowly (at first)
- About a second later, the car started surging...RPM oscillated between roughly 800 and 1000 rpm...I could also feel the car surging as it was reversing
- This occurred for about two or three cycles (i.e. it surged from 800 to 1000 rpm and back down two or three times)
- Afterwards, I stopped the car on my driveway for a minute trying to see if the problem would arise again...it did not
- Idling on the driveway was a bit rough
- On my drive to work, I noticed no rough idles nor any surging