Notes:
The voltage output from the Air Flow Meter (AFM) should be proportional to airflow. This can be measured on an oscilloscope and should look similar to the example shown. The waveform should show approximately 1.0 volt when the engine is at idle, but this voltage will rise as the engine is accelerated and air volume is increased, producing an initial peak. This peak is due to the initial influx of air and drops momentarily before the voltage rises again to another peak of about 4.0 to 4.5 volts. This voltage will, however, depend on how hard the engine is accelerated, and a lower voltage is not necessarily a fault within the AFM.
On deceleration the voltage drops sharply as the throttle butterfly closes, reducing the airflow, and the engine returns to idle. The final voltage drops gradually on an engine fitted with an idle speed control valve, as this slowly returns the engine to base idle as an anti-stall characteristic.
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