Here is the link to RealOEM page where the under engine covers and other bits are described. My 318ti doesn't have a cover under the sway bar to the pulleys and yet it looks as though there should be. But this link doesn't show anything like that. I have had to replace most of the pieces under the engine, previous owner ran over a tire on the freeway.
http://www.realoem.com/bmw/partgrp.d...06&hg=51&fg=75