Fuel Injections - air flow meters

There are a few different types of how air flow getting represented to ECU.
Directly:    K-Jetronic - Mechanical
                 L-Jetronic - Flap (or Vane) controlled. air flow pushes the flap inside the airflow meter box and wider the flap opens it means more air pushing it, so it would need more fuel for Lambda one. Disadvantages: spring on the flap becomes loose, restricts air. most early European cars, early Toyotas have it. there are two types of Flap Air meters: the ones that output around +4.5 V when idle and ones that output close to 0 when idle. this one is from Toyota MR2 and it outputs around +4.5V when flap is fully closed (at idle).

Testing:

according toyota manual there are 4 terminals: VC (+5V in), E2 (earth), VS (sensor output) and THA (temperature sensor)

       check the resistance according the manual.
wire the AFM up to 5V power supply and check the output voltage.

        

the voltage goes down as flap opens

checking it with scope

H-Jetronic - Hot Wire. The air flow sensor has got a titanium wire inside.Titanium wire gets hot when ECU puts current through it and changes it's resistance
Indirectly:  D-Jetronic - Map Sensor. Measures pressure in plenum chamber.