Originally Posted by workingonit

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.

• 1) I consider the "BMW expertise" of some forum members to be comparable, above, or way above mine, and value hints and recommendations given enough to try them. I consider (in my opinion) the value of their overall forum contributions as a way to judge (from afar) their skills...and sometimes they might have a slant or second opinion on a way to attack a problem that I'd be willing to try, so I do. As for experimenting with critical parts, that's something I have done many times, and know just about how far to go in that respect; a simple MAF swap isn't going to instantly destroy anything.
• 2) I've troubleshot this problem with no success for months; I'm beyond trying the same methods leading to similar (non) results. A small price to pay for a simple answer, given my limited diagnostic tools, and a limited "parts cannon" budget.
• 3) Who's to say what's original quality these days? Siemens OEM MAF from 2022 may not be as good as the original from 2001. There's no way to gauge them, no data sheets to refer to, no published specs.

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.

Agreed.

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.

• 1) I can't be sure that any MAF will work properly, so I am taking a chance on one that was recommended.
• 2) Troubleshooting without satisfactory answers leads me to try a new approach, i.e. "possible MAF under-reporting airflow", that wouldn't be necessary if there was data I could compare my tests to, so I am trying it.
• 3) No, my X5 isn't liable to burst into flames due to a MAF swap, but might be set afire if my wife catches me replacing
  • A) all vacuum lines,
  • B) intake boots,
  • C) fuel filter/pressure regulator/fuel pump,
  • D) O2 sensors,
  • E) SAP unit, etc.,
  any of which might be the real cause of the lean codes, but which also has eluded my testing, without exhausting all other possibilities first.
• 4) After many years of working on cars, racing cars, and working on machinery in my job, I agree with you about reputable brands being better, but have found that you don't always get what you paid for, and sometimes trying a substitute works out. In this case, not having a supply of BMW spare parts handy, nor the money to throw at it just now, I think it is justifiable in trying the cheap part for my version of troubleshooting.