[QUOTE=workingonit;1220721]But, would you try a new (and recommended) non-OEM MAF just to test the possibility that your original OEM MAF might be inaccurate, and might be the cause of the bad air/fuel ratio in the first place?
No, never. I don't consider a few recommendations from folks I have no idea of their skill level or even if they really purchased an item to be verification of anything. I don't experiment with critical parts. I would troubleshoot until I determined if the MAF was the culprit. If I find it is I would only buy a new MAF that was made by the original MFG.
I sure wouldn't/couldn't rent an OEM MAF just to test with, and I would never "buy" one, test with it, and then return it to the supplier (that's outright theft in my moral code).
I wouldn't send an MAF back. Don't know where that came from.

So, after X5chemist recommended the $23 non-OEM MAF earlier, I figured it would at least tell me if my Siemens MAF (age unknown) is under-reporting the g/s airflow, and triggerering my lean codes.[list][*]1) At best, I get a solution, after which I'd buy a new Siemens MAF to use (as soon as I get the $$$ to buy it, and keep the $23 unit as a known-good spare),[*]2) second-place result, with no change or very similar to the lean codes and g/s readings I'm already getting, I've got evidence that my OEM sensor is still OK, and I've got a spare, and[*]3) worst case result, as the $23 MAF shorts out my DME, and the X5 burns to the ground, then I made a mistake and I lost $23 and my X5 (but proved those doubting the reasons to get a cheap sensor to be infallible).

If you can't be sure the $23 unit works properly it won't verify anything. Troubleshoot. Troubleshoot. Verify the source of the problem. If you are willing to take the risk of burning your X5 to the ground, that's fine. I've learned over the years that buying new parts from reputable brands is a far better route in the long run. I go through MAFs quite often because of the engine mods. I have a spare new MAF to slap in when needed. Even then I troubleshoot to verify the MAF is bad. I don't use the new MAF for troubleshooting.

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