On the 330i it's supposed to stay open on idle. It closes when you drive, but I'm not sure the exact conditions.
The 335i closes it at idle.
AW/Terra | ZSP | ZPP | ZCW | iDrive | CA
Mods: BC BR | OEM Blacklines | M-tech rear | custom dual exhaust | M3 steering wheel | BMW SSK | ZHP shift knob | BMW Performance rep spoiler
Varrstoen ES1 19x9.5+20 Front, 19x11+25 rear