EDIT: WARNING, I would advise to only try this if you are having problems with your engine (eg lumpy/rough idle etc...) and suspect it is your MAF.
My first run after cleaning as below produced a faulty MAF
The car had stood for a week or so since I cleaned the MAF and car started fine and ran perfectly for 70 miles. But on stopping to refuel the car would not restart
The car would actually start but not rev and idle at 500rpm for a second and die out. Turned out to be faulty MAF so I had damaged it by cleaning
It is worth noting though that the car ran fine with the MAF disconnected, just a little down on top end power but ran smooth.
So if you suspect MAF problems I would suggest just disconnecting the MAF and taking for a run (engine management light will be on but will cause no damage as car uses a "default" MAF reading). If the symptoms go then you know its your MAF and you can have a go at cleaning
On fitting a new MAF car ran "rough" for a minute hen settled down to normal. Engine Management light stayed on for another 20 miles but was off net time car was started
Although my car seems to be running fine I've read about plenty of people who have had problems that have resulted from faulty MAF sensors.
So I decided partly out of curiosity and partly for preventative maintenance, to clean the MAF sensor on my S54 engine.
Please note that the MAF sensor is c£200 to replace so care should be taken to handle it with respect
On the S54 engine the MAF sensor is connected to the rear of the airbox. On the S50 it is a slightly different design and fitting but I presume just as easy to clean.
Here is the RealOEM LINK
for an S54.
The part number is 13627839014 and is common to a lot of ///M series models (ie e46 M3; M5; M6; Z4m)
Note that you will need a special "security" Torx drive to remove two securing torx screws.
Here is the MAF sensor in situ:
Here is a security Torx Screw and driver. Note the requirement for a "hollow" in the drive meaning a normal Torx drive will not fit
First of the two securing screws being removed:
You then "pinch" the electrical connector block and pull it off:
The MAF Sensor removed from the car.
Note the sensor wire. This works by measuring the amount of current required to keep the wire at a set temperature. Air flow over this wire affects the current required. Even though this is held in the airflow after the air filter it can still get a build up of dirt deposits (or oil off an oil based filter medium) which affect the accuracy of the air flow reading and hence the fuel mixture the engine uses. This not only affects fuel consumption but can result in perceived "flat spots" in throttle response.
On close inspection this wire did not seem to exhibit any contamination but I decided to clean it anyway.
I had sourced some MAF cleaner from eBay (following recommendations on other forums)
You simply spray this onto the MAF wires. Note do not touch the wires directly, just with the cleaning spray. You can flood the area to ensure any deposits are washed away.
The fluid evaporates very quickly. Here is a pic stright after the process following a minute of "wafting" in the air.
It is then left for 10minutes to dry completey and fitted back to the car (do not start the car until completely dry).
Note which way the MAF is refitted:
So its a simple 10 minute job.
Car started fine but I did not have chance to drive it
I don't really expect it to make much difference as the car was running fine anyway but hopefully this will help people who are experiencing some of the problems noted above to see how easy it is to try this solution yourself (ie no need to take to a garage to get your MAF cleaned). Given how simple this is there really is no reason not to add it to an inspection II type service.