I live in London and so my K&N has to filter a lot more particulates and guink than most. As an indicator My cabin filter is blocked at 10k miles
K&N's actually filter to a smaller particle size (Acording to their literature) than the Ford Standard filter so no issues there and my intake tubes have been a lot cleaner since I binned the Ford intake system and swapped to the K&N. I have yet to see any oil from a K&N even on the inside of the K&N filter so I doubt this contaminated the MAF. You have to really over oil the filter to do this
My old MAF was spotlessly clean when I replaced it, it just didn't work. Probably due to 105K miles of heating/cooling cycles rather than contamination
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Mad Moles Mondeo Madness 2L Zetec, Cams, Stage 2 head, Valve work, Powerflow, Unichip, AEM Ram, K&N, Ecotek, 75mm Lower etc.
192 BHP, Faster than a speeding Duratec!