You do not state whether you fitted a new air cleaner for test.If you did not buy a new one
buy one now of the same make and weigh them both,this will give you an idea of how much work
the original filter has done.
Regards Ian.
if its mk2 or mk2.5 the 3 pin thermo sensor under the oil has reduced emissions for me dozens of times. I actually proofed this more then once, byu failed MOT/NCT tests ,replaced sensor, passed straight away without any other work!!