Blower motor with a mind of its own is often times a failing blower motor resistor/final stage unit. A search should turn up dozens of threads.

The cabin microfilter is in a slot, near the firewall, under the hood.

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12 E70 3.5i xDrive
03 E46 330i ZHP
01 E53 3.0i
98 E36 323is
12 Audi A4 Quattro
79 Triumph Spitfire
73 MGB