BMW has chose to put these dam CDV's in every manual car they make. Even M cars. (there was some hot debate on this even for the e9x M3. But I believe all of the cars have them). Sometimes they change the amount of the restriction inside the CDV. But otherwise all of the cars have them. Best thing to do is take yours out and inspect it. I bet you have a venturi/jet inside of your CDV.
Acording to RealOEM.com all 135i's and M1's use the same CDV valve... #21526764872
Actually this very CDV is used in quite a few BMW's...
http://realoem.com/bmw/partxref.do?part=%0921526764872
Bottom line is take your CDV out - you will be much happier without it!!
