BMW Repair: rough idle after car has been sitting for months, battery discharge, cold start

Question
my 02 M3 has been sitting for months ~5.  When I start the car, it idles rough for a few seconds.   I don't hear any noises.  Could water have condensed in the fuel system, is my gas old?..

Thanks to all for answering so many of my questions

Answer
David, water in the gas is a possibility after 5 months. Has the car been sitting indoors, outdoors? Take a fluid sample and see if there is any water or if the gasoline has started to seperate. Honestly the rough running on cold start for a few seconds is pretty normal for your S54 motor. That car is meant to be run. Just make sure you drive it frequently or at least drive it around the block to avoid battery discharge issues.
-Evan