BMW Repair: 2000 528i bmw Idle, vent valve, air leaks

Question
2000 bmw 528i with 160000 miles. sometimes in the cold wether, the car (engine) vibrates violently like a washer machine on spin cycle. after about 20 minutes, all is back to normal.Dealer does not know what is causing it, or believe me.
Thank you for your time.

Answer
Tony, check for air leaks in the intake system especially at the throttle boot. Have you replaced the spark plugs at 100,000miles? Have you left the car at the dealer for them to replicate the condition? You could try a DME (engine computer) reprogramming, but with a car with that many miles on it, it is probably something physical as apposed to software. You could also check the crankcase vent valve.
-Evan