BMW Repair: idle fluctuating, crank case vent, oil filler cap

Question
2000 328i, 100K miles
When sitting in Idle, about every 8 seconds the RPMs drop quickly to about 500 RPMS and then jumps back to 1.2K.  Occasionally when cold, it will actually stall.  Any ideas?  Seems to be more prevenant when cold and on first drive of the day.

Answer
Tim, check the intake boots for cracks and air leaks around the idle valve off shute. Also crack the oil filler cap open with the engine idleing. If there is a huge amount of vacuum or a strange noise then the crank case vent valve (PCV) will need to be replaced. Either will cause an unmetered air leak.
-Evan