It MIGHT be a Vanos, but it doesn't sound like you ar experiencing any of the telltale signs of vanoe issues......
What are the symptoms of a failing vanos?
Overall loss of torque and power, particularly in the lower RPM range, < 3k. Bogging then surging at 3k RPM. Uneven power distribution and RPM transition. Engine hesitations in the lower RPM range, < 3k. Louder idle and intermittent idle RPM hiccups. Difficult takeoffs. Loss of power and bogging when AC on. Increased fuel consumption.
Double vanos cars with the M52TU engine (98/99-00) experience cold weather cold start idle jolts and possible stall.
Usually worn Vanos will nake an aweful racket and are quite noisey. I'd start by looking for a vacuum or air leak in the intake or PCV system. Use combustion chamber cleaner (while running) and spray around ALL intake components and vacuum lines. Listen for canges in engine rpm. Make sure to check the PCV valve. The main house leading from the bottom is prone to failure (overheating makes it break down) and will cause your symptoms....
ONLY after you've confirmed none of these are the culprit, then start looking @ the vanos. Eliminate the obvious and then look for the less obvious.