Error code 17544/17546 - A8 3.7 Quattro EZ 9/97 (2

Hello, everybody.

I always have the above error code for my vehicle. I've already replaced the air mass meter with a new one. At first, I thought the mistake was gone, but after reading out again today, he's back.
Any of you have an idea. It concerns both cylinder banks:
Oh, here's the longbed description of the error codes:

Fuel Trim: Bank 1 (Add): System too Lean
Fuel Trim: Bank 2 (Add): System too Lean

Would be great if someone could help me.

Have a nice evening
Jochen Kr.