AFM101 : Inside the Air Flow Meter

 
   
Connector View

An airflow meter is used on on the 1990-1993 miata. It has three functions, all which are determined by electrical sensors.

1. Airflow On/Off
If the engine is running, it is sucking air. The AFM will close a switch when this happens. Two contacts are used for the switch. The switch is closed to keep the fuel pump running.

2. Airflow Rate
As the air flows thru the AFM, it moves a flapper.The position of the flapper is converted to a voltage (about 3.3 volts at idle). when the engine pciks up speed, it sucks more air, the flapper moves, and the voltage on this pin drops.

3. Air temperature
A sensor inside the AFM changes resistance with air temperature. This determines the voltage on this pin. It goes down as the air gets warmer.
Top View of the AFM.
Electrical View of the AFM

This shows the circuitry inside of the AFM, and its electrical equivalent.

Front View showing the air flapper closed and partially open

The little peg in front of the swing door is the thermister casing.
I'm neither a certifed auto mechanic nor a trained Mazda technician. The information on this page is my own interpretation and may be flat-ass wrong. Use at your own discretion and risk.