E30/E28: Faulty AFM (Air Flow Meter) repairs, worn carbon-track quick fix

** FOR ADJUSTING AFM AIR/FUEL RATIO SEE THIS POST **

The AFM or Air Flow Meter uses a metal flap that is opened air entering the engine to move a brass arm up and down a carbon-track. The position of the arm along the carbon track alters the electrical resistance through the circuit and this lets the ECU know how much air is coming in, so it can deliver the right amount of fuel to the injectors. The E30 uses a BOSCH AFM unit, also used in many other BMWs with Motronic or Jetronic injection systems.

The analog electrics in the BOSCH AFMs rarely ever fail, but there are two areas that are failure prone after higher mileage - a worn carbon track and a faulty air-temperature sensor.

BMW Response Vehicle Owner's Manual

I can't imagine many people have this in their book-pack. BMW supply cars directly to UK Police constabularies, so this is their in-house user manual for controlling the lights and sirens no less. It shows even the switch-gear being factory fitted with buttons to match the BMW fascia, though I am not sure what level of spec mine had. I guess this is another easter-egg gift that comes with owning an ex-Police car, along with tons of extra wiring and air-con that stinks of sweat...