What the hell *is* an AFM?
In stock form, the 22RTE uses an air flow meter, aka AFM, flapper door, or vane-type meter, to measure the amount of air entering the engine. Please get this bit of terminology right, as an AFM is not a MAF (mass air flow meter), nor is it a MAP (manifold absolute pressure) sensor. An AFM measures air flow through what is essentially a mechanical process, where incoming air deflects a flap in an enclosed space. More air coming in = more deflection of the flap. Crudely speaking, a potentiometer is connected to the flap, and as the flap moves, the potentiometer moves, and this shapes the electrical signal that is sent to the ECU. To control the movement of this flap/aramture, the AFM is fitted with a flat-wound spring that is used to apply tension to the flap. This spring is held in place, and adjusted, via a plastic gear and a wire “holder”. When this gear is tightened (turned clockwise) relative to the flat wound spring inside of it, it becomes harder for the door to open, and this tra