workingonit,
Mine still has the same MAF from two years ago. I need to check my spreadsheet. I think it has over 25k miles now. I've almost had my X for 27k miles. The codes above are the first since installing the cheap MAF. The codes were caused by me. The loose connection past the MAF and loose filter clip.

What are your BMW specific codes? My Foxwell Pro 520 gave me E3/34. Codes are caused by several possible symptoms. The BMW ECM is "smart" enough to know the cause of generic ODBII codes, at least for the codes above.

If you like, I'll send you my OEM one. It's in a box collecting dust. If the MAF on mine fails, I'll replace it promptly. I think I have enough knowledge to test a MAF sensor for replacement.

code history; a good Siemens-VDO MAF to test with??
 

Here's my "generic" code list, from the 3.75 years I've had the X, not counting therecent codes associated with the failed battery last fall (none current, or even in the last two years):

P0171 - fuel system too lean-bank 1
P0174 - fuel system too lean-bank 2
P0313 - misfire detected with low fuel
P0365 - camshaft Position Sensor 'B' Circuit Bank 1
P0369 - camshaft Position Sensor 'B' Circuit Intermittent Bank 1
P0505 - idle control system, idle speed not plausible

and the pertinent Foxwell/BMW-specific codes for the lean condition
Attachment 84686

If your old OEM MAF sensor is proven good, sure, I'd love to use it for testing. andrewwynn once offered to send me his spare, once, but it didn't happen?? I have no baseline of comparison, without trying a "known good" (non-Chinesium) MAF, first. PM forthcoming.

BMW codes have taught me code symptoms are beyond their description. The E3/E4 are rich fuel codes. Only because too much air is being detected (by O2 sensors). The ECM is adding fuel to try and reach ideal stoichiometry.

The MAF has been running for 25k miles. The OEM one I'm sending has 143k miles on it. I took it off for cleaning and never put it back. The replacement has been working so far.

Undetectable vacuum leak and lazy after-cat O2 sensors are all I've been able to zero in on, after all this time. And the fact my original MAF was wacky to begin with. Starting in Nov.'21, it was first noticed to be drastically underreporting airflow, so I cleaned it, to no effect, and started my hunt for leaks, etc. The cheap $20? Chinesium MAF you recommended gave me better airflow and fuel trim readings immediately, but not quite perfect, and that's the way it's been, ever since, despite dozens of hours spent fiddling with it.

My OEM MAF had 210000+ miles on it when removed, and I tried it again 2k miles later (it went completely nuts), so I never knew if it was bad from the day I got the X (at 210008 miles). It'll be good to compare fuel trim and airflow readings I've been getting with the cheap MAF to whatever I'll get using your proven good MAF. Maybe I'll solve the problem using it, I hope.