Two things are causing your problem: 1) worn engine mounts 2) cracked intake boot.
When you start to take off in first gear and shift to second, the worn engine mounts are allowing the engine to rock side to side. This in turn is opening and closing the tiny hairline cracks in your intake boot which is causing the car to misfire/buck.
You can easily check this by first leaving the hood open and have someone drive forward a few feet while you stand outside of the vehicle and watch the engine move, and second by purchasing a can of brake/parts cleaner(NOT CARB CLEANER) for 4 bucks, then with the engine idleing, spray brake cleaner on and around the intake boot and nearby vacuum lines.
I'm talking about the ribbed rubber elbow just downstream of your air flow meter. Don't be shy with the brake cleaner, hose the whole thing down and try to get the bottom side of the boot as well. Once you hear your engine rpm's fluctuate(ramp up), you'll know you've found your leak.
Temporary fix, wrap the boot with several layers of duct tape. Then ASAP order new engine mounts and intake boot.
You can find the part numbers on realoem.com(make sure you order the correct boot for your year/options). GetBMWparts.com and pelicanparts.com are going to be your best sources for OEM parts. They have the best prices, fastest shipping and best service hands down.
Again, only use brake/parts cleaner to perform the test. Carb cleaner will dry out plastic and rubber parts and it's not as flamable as brake cleaner so it probably won't cause the idle to fluctuate like the brake cleaner does. Best wishes!
Last edited by cooljess76; 05-24-2012 at 06:27 AM. | 
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