I just ordered one from Amazon, will be here by Wednesday. I currently have the maf unplugged because it's running better without it. Trans fail safe light is on but my wife is only driving it to pick up/drop off kids from school.

just as I was extolling the virtues of the cheap MAF...
 

What fuel trim readings are you getting without the MAF sensor plugged in? or is it just feeling better (a seat of the pants impression)? I've been monitoring my trims everytime I've turned the X5 on, since summer of '21, though not with the MAF unplugged. I might try that soon, because I've become worried about my current fuel trims' trending toward the upper end of the scale, not towards zero, which would be ideal.

I posted a photo (see post #11 https://xoutpost.com/1228927-post11.html of what my fuel trims were last December, after finally installing the Cheap MAF, passing inspection, and finally after getting a few miles at highway speeds (Italian tune-up), that brought my trims down to a comfortable level, and my overall fuel mileage up

Since then, I've only driven the X5 a few times, seemingly at the worst times for traffic, and at the low speed stop & go cycle that made my fuel trims rise before. And today, I did a shopping trip (four stops, 15 miles total) where the long-terms rose from about +6 (they were already that high from the previous 3 trips over 3 months) to a +10 on both banks, as I parked it at home.

I used Torque Pro (which was displaying the data on my Android tablet, as usual) to check for any fault codes, or emission problems, but it found nothing. I'll scan tomorrow with my Foxwell for the same, and observe live data as well, and if nothing shows up, I'll try the laptop with INPA (still learning how to use it, so ??? results are expected). If I find nothing obvious, I'll take a three-step approach to learn more, and/or get better readings.

• 1) remove the cheap MAF, clean it with MAF cleaner, reinstall it, and read the results. If readings improve, then problem is solved. If not, then
• 2) I replace it with the unused cheap MAF I just bought, and again, if readings improve, the problem is solved, or
• 3) leave the MAF sensor unplugged, and see if my M54 will run decently without it, and see if the fuel trims get better.

Of course, this happens "just as I was extolling the virtues of the cheap MAF". It could be unconnected to the MAF itself, but to either my driving patterns being abusive to a good engine's health (slow speed, stop & go, lotsa inactivity), or to an underlying problem I've yet to put my finger on, after almost 18 months of trying. The X5 never misses a beat, starts easily, no misfires or driveability problems, nothing at all. I'm pretty sure you'll have better luck finding your problem....

I haven't checked the fuel trims with the maf unplugged.
When I replace the maf on Wednesday, I will take it for a quick boot around the block before I swap it in and check the new values with the new one. The issue is now that the trans fail safe mode is on so performance and driveability are impacted.
It definitely runs better with the maf unplugged. When it's plugged in, it idles like it's ready to stall.

Trans fail safe will run only in 4th gear. Definitely not something you want to do repeatedly. Which engine? Must be 3.0 off disa valve. I rebuilt both mine and wife's and didn't have new gasket so I used oatey fasttape Teflon tape and it worked wonders definitely seal that disa tight

Yes I have the 3.0
And the "trans fail safe" light comes on when the maf is unplugged but it still runs fine and shifts through all the gears. But you can definitely feel that the car is restricted in some way, but still runs better than having the maf plugged in. Mind you, my wife is only using it to pick up and drop off the kids at school, so only a few km a day. Also did the same with my disa valve, its sealed up tight. I believe it is leaking through the vein, not the area where it connects to the intake.

more MAF experiments
 

I ran mine with the MAF unplugged today (ran OK); Torque Pro shows the long-terms as zero and the short-terms usually pegged-out at -28.12%. And the "trans fail safe" stays on until the MAF is plugged back in.

I cleaned the MAF, as I said I would in step one of my plan, then skipped to step three to zero the long-term fuel trims, then encountered problems using my Foxwell, then a no-start condition, so I don't have new data, other than the cleaned MAF works as good as ever (when freshly installed). But I did find that the MAF wasn't tight in the intake tube, on either end; I know I fully tightened it when installing, so I'm going to put silicone tape on both ends, to seal it better.

Update: received the new MAF today. Installed and let the car warm up.
Trans fail safe went away and idled smoothly. Until the check engine light came on with all the same wonderful codes that were present before:
203 lambda regulation limit bank 2
227 lambda controller deviation bank 1
202 lambda regulation limit bank 1
242 misfire 5
243 misfire 6
241 misfire 4

So, not the MAF causing the issue. Back to the drawing board: not a significant vacuum leak that I can find and not the MAF. My guess now has to be oxygen sensors? I haven't changed the upstream sensors yet, but I have changed one downstream. Also going to grab a can of carb cleaner and double down on the leak search. Smoke test was amateur and I possibly couldve missed it. Though I know it's not the usual culprits, it may be hiding.

Multiple cylinder misfire suggests weak coil and/or f end of life plug. I replaced a couple weak coils on wife's m54 e53 a while back chasing one after the other cylinder misfire. After changing 2 out and got another random misfire I ran some Lucas injector cleaner and the errors stopped and with semi annual Lucas treatment they never came back.

Voltage fluctuation will cause the transmission error you are having so watch realtime voltage and make sure it's stable especially when you throttle off to come to a stop.

Odometer?

Swap coils on any cylinder repeatedly misfiring but first check the voltage. If your voltage isn't solid 14.4 ± 0.2 all your problems can be just from the alternator.

Have you had any intermittent trifecta that came on especially when slowing to a stop that clears itself? That's alternator.

The fuel trim situation does suggest O₂ sensors so I would replace both pre cat sensors with oe models

Another update: so the codes and issues are now gone.
I had a friend who is a bmw "guy" come over with his mechanic diagnostic computer and have a look at it. He did a bunch of functionality tests and noticed something wasn't working that required vacuum and that's how he found a loose hose.
All in all, the MAF was the issue all along but with everything I was looking at, i clearly needed a fresh set of eyes to see the small thing I missed when I reassembled things.