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The left pipe has a flap that closes off the outlet upon start up, and once the engine is warmed up it will open and both pipes are flowing exhaust.
If you start the car and get out and listen, maybe even peer into the left pipe from a few feet back (don’t inhale the fumes) you can hear/see the flap open.
Also, it isn’t smoke, its water vapor. at least...I hope your car is not smoking lol.
many people disable the flap (known as the “golf tee mod”).
The flap is pretty much there to reduce noise at low RPMS
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Gone but not forgotten
14 335i
12 335i 6 speed
11 328i
06 330i
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