Air Flow Meter
All engine air is drawn through the air flow meter. The meter contains a tunnel with measuring flap and dampening flap (offset 90° on same casting). The measuring flap swings in air stream against pressure of a spiral spring and is connected to a potentiometer.
The potentiometer transmits an electrical signal determined by measuring flap position to inform the ECU of engine load. See Fig 1 . In addition to monitoring the air flow, the meter also controls fuel pump operation and idling. At idle, the measuring flap is almost closed due to spiral 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.