A cabin micro filter on a BMW1 series is an air filter for the inside of the car. It is under the dash and catches dust and other airborne particles.
The microfilter is the filter for the air that enters the cabin of the vehicle.
On the E39, there's 1 on each side at the rear of the engine compartment. They're located inside plastic boxes.
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You do not specify what year. With the air filter on the E36 (approx 1992-1999) you must remove the glovebox. After the glovebox is removed you will see the air filter on the left side (on an RHD car)
The 2012 BMW 1-Series has 24 valves.
The 2008 BMW 1-Series has 24 valves.
The 2013 BMW 1-Series has 24 valves.
The 2011 BMW 1-Series has 24 valves.
The 2010 BMW 1-Series has 24 valves.
The 2009 BMW 1-Series has 24 valves.
BMW series are the type of sedans that they have. 1 series, 3 series, 4 series, 5 series, 7series