i just replaced that an pump last year... are there 2 of them?
you were right on about it though, it was an air pump... for them to put my new rotors on, fix the air pump, and an oil change (since it is due and has been there over a week now - $1202
less 10% for bmwcca - $1082.8
plus, I spent $700 on new coils! ARGH!!!! this thing better run like a dream when I am done...