[Richard L]

The rocking of the turbine wheel in the sensor is the most likely cause of the false readings.

The turbine wheel is magnetised. Polarity flip when rotates. Producing electrical pulses from the Hall Sensor Chip inside the "C-clip."

Depending on the orientation of the turbine wheel relative to the Hall sensor, a slight movement will produce a pulse. If the position is very closed to the flipping of the magnetic poles. Slight vibration will produce false readings.

By rotating the c-clip diametrically, you can avoid false readings. Or place the FAV away from vibration.