The only thing I know of is the swirlflaps in the inlet manifold.
If it's an early model there could be issues with this. I know a lot of ppl here i Europe that has got them removed.
The problem is that they can come off and be sucked into the engine with an engine replacement to follow....
Otherwise it's a great car. I love mine!!!!
'06 E91 330dA Sparkling Graphite|19" AvantGarde M359 Satin Black|335i brakes|Bilstein B16 IRC|Powerflex|GroundControl|Wagner|Ecotune|Turbo Dynamics|Zimmermann