This is exactly one of the symptoms the 335i owners on E90POST have been complaining about. The lag was introduced by V29.2 software which operates the wastegates differently at low revs vs earlier s/w - the lag seems ok when cold but is apparent when the engine is up to working temp/
The post is 60 pages!!!!
http://www.e90post.com/forums/showth...147781&page=60