Interesting observation about the speed difference in voltage changes on each bank. I'm very interested in the results, definately let us know!

So I was travelling last week, and did not manage to confirm the order for a new MAF sensor yet.
Then, while waiting on the airport, I stumbled on a forum thread (forgot which forum, and if it was an old or new post).

Anyway, the poster advised to check on the connection of the MAF connectors, especially the pins.
My connector showed perfectly clean, and I was already a bit disappointed.

Nevertheless, I bent the pins just a little bit down to have some better contact pressure.

Guess what; Long term Fuel Trims dropped from -15 back to ~-5 at warm idle for both banks, and the MAF reading itself dropped just below the factory advised value for idle.

I still need to make a ride, but based upon previous readings, I am confident that I will be back at 'around zero' readings once I give it a bit of gas.

The downstream O2 sensor still shows its weird behavior, so I will replace that one, but I just saved some bucks, good feeling!

Thanks for all the advise, I hopefully will get back here one more time after the new O2 sensor is installed.

EDIT: Quick test ride confirmed the values are back to normal, both for the Short Term and Long Term Fuel Trims.

Good news!

Excellent!!