A MAF Sensor determines the amount of air entering through the engines intake.
How It Works
A common form of MAF sensor used in vehicles now is the Hot Wire System, basically a wire that is suspended in the vehicles intake system that is heated using an electrical current.
The Electrical resistance increases as the wire's temperature increases, this limits the current flowing through the circuit. As air flows over the wire the wire cools decreasing resistance meaning that the current flow increases across the circuit which in turn increases the temperature of the wire until it reach's the original preset temperature.
The current required to heat the wire is proportional to the mass of air flowing past the hot wire, the IEC (Integrated Electronic Circuit) converts the current flow to a voltage signal which is sent to the ECU, telling the ECU how much air is entering the intake so that the ECU is able to determine the amount of fuel to discharge into the cylinders.
Incorporated into the MAF Sensor is also an intake temperature sensor which allows the MAF Sensor to take into account the change in air density due to the increase or decrease in intake air temperature
Problems That Can Arise Due To A Dirty Or Malfunctioning MAF Sensor
Engine Stalling During Idle
Rough Idling
Poor Acceleration
Hesitation At Acceleration
Engine Surging
Just to name a few
Tools Required
I needed only two tools and a can of CRC contact cleaner for this job.
A Flat head screw-driver
Torch (just for a better look in at the MAF Sensor
Removing And Cleaning The MAF Sensor
I chose not to remove the MAF Sensor from the upper air cleaner cover as I didn't see that it was necessary.
Firstly Unplug the MAF Sensor Connector
2. Using Screw Driver loosen the hose clamp which secures the intake hose to the upper air cleaner cover
3. Remove hoses that are clipped into the top of the upper air cleaner cover
4. Un-clip upper air cleaner cover and remove from engine bay, wriggling it from the intake pipe if necessary
5. Inspect the MAF Sensor (inside the pipe of the upper air cleaner cover) with a torch (I found that the back of my hot-wire was nice and shiny whilst the front was covered in a black carbon like soot (Probably fine dirt particles)
6. Using the Contact cleaner thoroughly spray around the front and back of the MAF sensor to remove any built up residue (mainly on the hot-wire)
7. Once you are confident that the hot-wire looks clean and shiny allow it to sit somewhere in the shade for approximately 30 minutes before re-installing onto your car
8. Re-install in reverse the reverse order that you took things apart
Diagram of the engine bay showing the location of the MAF Sensor.
A write-up on cleaning the O2 Sensors for the TT to folow
I agree with you Jovan, I only used the paper filters in mine 
