Yes there is a microfilter in your Bimmer. I am not sure where in your model (E38 I believe), in the E32 it is located almost behind the glove box and adjacent to the center heater duct. I have procedure for E32 but not sure that is the same so you may wish to vist roadfly.com and the E38 board, register (it is free) and ask this question on that board. Or, you cn Eamil me and I can send you a text and photo how to on the E32.