The reason the OE MAF sensor is considerably more expensive than the aftermarket ones is a simple one.
The original unit uses a platinum hot film anemometer, i.e. it is a constant temperature thermistor arranged in a wheatstone bridge.
So this is how it works
Power from the ECM heats the thermistor up to a predetermined temperature
TH.
A airflow with velocity
V and ambient temperature
TA cools the heater down until an equilibrium between the electrical heat and the thermal heat loss
Q is reached.
The higher the velocity
V and the difference
TH-A=TH-TA between the thermistor temperature
TH and the variable inlet air temperature
TA, the higher is the heat loss from the platinum hot film thermistor.
The inlet air temperature
TA, which can change, so
TH-A is measured with an additional inlet air temperature sensor which is part of the bridge circuit in order to compensate changes in the ambient temperature automatically.
Basically this speed, volume and temperature of the incoming air charge is calculated by the ECM based upon the heat loss of the platinum hot film thermistor, and the fuelling is adjusted accordingly
Aftermarket MAF sensors generally speaking are cheaper because of the metal composition of the heater thermistor, and quite often the inlet air temperature components are omitted, meaning the output offset voltages are misinterpreted by the ECM
This is one case where buying cheaply certainly means buying twice, and when looking at the live data, I can spot a mile off if a car is fitted with a generic MAF sensor, or indeed a Pierburg MAF sensor, which incidentally does not include any form of inlet air temperature sensor
So if your MAF sensor is definitely knackered, and yes unplugging it and seeing an improvement in performance is not a reliable method of testing, save yourself the wasted money of buying anything other than the Bosch unit.
Like Russ has said, most if not all aftermarket sensors have been trialled and found to be lacking.
Brian
