I already bought the parts I needed for the on/off MAF reset switch, and was about to assemble them for installation, then reconsidered.
I will wait until after the state inspection (safety & emissions...my '01 is two years away from not having to get the sniffer test, anymore) before I do any experimental work on the MAF system. I'll use Liqui Moly Catalytic System Clean 7110 and Premium gas to prep the fuel system (not the Jectron 2007 that I usually use), drive about 100 highway miles to make sure that all the emission monitors get set, and drive directly to my usual inspection station (before the fuel trims go wacky again). Then, I can experiment.
Researching and reading. I read a lot this past week, seeing how people custom-tune their MAFs, MAPs, and even the old mechanical Air-Flow monitors, from the 80's 'til now, Chevys-Toyotas-Ferraris, all of them. There's actually less info concerning BMWs than most other makes, of course, since BMW wants it that way.
I wish I had been trained in electronics, as most of what I read was basically Greek to me (I might've understood Greek better!). But, I did find a possible way to make minor tweaks to the MAF signal that tells the DME what the airflow is, by tricking the system, using a device to adjust the heated element component in my MAF sensor, without adding resistors or using a custom air intake tube.
If I was to lower the temperature of the hot-film (similar to the old type hot-wire) heating element, it would make the MAF act like there was more airflow than there actually was, then the resulting signal generated and sent to the DME would naturally enrichen the mixture without having a false lean fuel trim reading do the same.
I originally thought my lean fuel trims (triggerring P0171, P0174, and eventually a CEL) were caused by my Siemens-VDO MAF under-reporting airflow.
I still think it does. The cheap $20-23 Amazon MAFs I've been using for two years, give better airflow readings, but not perfect. So, my idea here is to further trick the system, by using another cheap device (a "Buck-Boost" converter), to fool the DME into thinking that airflow is greater than in actuality. And maybe quit trying to set lean codes in the process.
I previously used a diagram (in post #1) that was wrong, but found the correct diagram for my '01. It shows that if I would insert a step-up/step-down voltage control ("Buck-Boost" converter) in the 12v wire just before it enters the MAF, then I could use it to either raise the temperature of the hot-film heating element (which would cause a lean signal to be sent), or preferably, in my case, lower the temperature (which would cause a rich signal to be sent).
I see that there are all sorts of circuit protection in the units I've investigated, so no damage to the circuits upstream nor downstream of the device should occur. Of course, I'd also use a fuse ahead of the device, anyway. If, perchance, one of my three MAFs were to fail, then I'd have the excuse to try a mid-grade MAF (from Hella, Bremi, Pierburg, or even Delphi...I'm not ready to buy a Siemens VDO, until I fix the phantom problem first).
I am currently looking at three converters, from $25-34, that I might try. I have no idea what actual amperage/wattage rating is needed, but I've wasted money before...trial and error is often expensive. Of course, I'm watching many videos on how to set them up, but it'll take me awhile to get the gist, if ever.