Air Flow Meter
All engine air is drawn through the air flow meter. The meter is basically a tunnel with similarly shaped measuring flap and dampening flap (offset 90° on same casting). The measuring flap swings on an axis in air stream against pressure of a spiral spring and is connected to a potentiometer. The potentiometer transmits an electrical signal to inform the ECU of engine load. See Fig 1 .
In addition to monitoring the air flow, it controls engine idle. At idle, the measuring flap is almost closed due to spring pressure. An idle air by-pass receives air from main air flow through a small hole, the size of which is controlled by the idle mixture screw. This adjustable air by-pass influences CO levels at low engine speeds.