If you are doing a RESET then the radio code will be required before hand mate, disconnected battery scenario. You should have a credit card thing in your plastic owners manual sleeve with the code on.
The airbox shouldn't really move much. It has one securing bolt attached to the battery tray area and two plastic lugs that go into rubber gromets... Imagine the vibrations that it goes through in the rev range and rough roads etc.
First thing to do is to remove the plastic induction pipe to the MAF and airbox.. Now remove the top lid of the airbox.
Pay particular attention to the two metal spring clips.. are they tight to remove?
Now pay attention to the two plastic lugs that the top slides into.... Any broken or worn?
Wearing due to vibration will make these lugs thinner than normal in comparison to a new airbox... That's why its so important to make sure that the whole airbox is secure and tight.
Resin or even some insulating tape wrapped around can be used to beef up these lugs if they are thinner so that the lid has more downward pressure on it when all clipped back into place
Have a look at the piccy.... the red sections are what need to be nice and tight when the lid goes back on.
Now have a good look at the paper air filter itself.... It should be nice and clean on the top.. Any dirty marks show that unfiltered air is getting through... Replace it ... For the cheap cost and peace of mind...
Many garages and service departments don't change them for years, just inspect them.... And there is also the fact that a bad "spanner monkey"
was given the job of checking it.
Pay attention to the orange foam seal... Again, is there any signs of dirt on the top sealing edge? If so, then it's the failure of the securing of the airbox lid spring clips or lugs... It should have a nice tight seal top and bottom of the airbox lid (marked in green)
Some temporary Hylomar instant gasket seal can help if the air filter wont settle in the reccesses properly.
Give the bottom of the airbox a good vacuum to get out any big bits of dirt etc.... This shouldn't affect the MAF if the paper filter is seated properly but it won't hurt to give it a clean anyway.
Now while you have the lid off make sure you secure the bottom of the box in its lugs and bolt hole properly... Refit it all back together in reverse
While you are at it go to somewhere like B&Q and buy some cheap jubilee clips 65-85mm and replace all the crappy spring type clips for all the induction /MAF all the way from the airbox lid to the throttle body... The spring clips only last a few removals and then loose tension...Jubilee clips don't!...
Don't forget to give your throttle butterfly a good clean up (plenty of tutorials on this site, just use the search facility)
Not sure if the 147 is fly-by-wire but don't move it by hand, just get a helper to press the throttle pedal while you spray it with the carb cleaner.
If you really want to give it a good clean out, unbolt and remove it but be aware, it will need a fresh gasket seal when re-fitting.
Don't touch the butterfly just spray it from the front and back, let the cleaner do its stuff and leave for a while to soak and evaporate.
Again, not much of a cost but worth the peace of mind... Do the ECU reset and drive/wait... The TS will be back to it's former glory soon enough
Now there should be no reason why your maf will get dirty again... Good luck mate and let us know how you get on