Failed motor mounts are easy to check for, but I would be looking for vacuum leaks first, and then at the idle control valve, especially on the 3.0. It raises idle speed, and many posters above seem to have too low an idle speed when in drive.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue