The MAF is a critical part of the fuel/air mixture system. I never install an MAF that is not an OE or OEM part. My guess is the scope of remanufacturing and selling an MAF for $29 is that it has only been cleaned, maybe not even with MAF cleaner.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas