Lean Code - Help Understanding Fuel Trims

[AliBaba.BoomBap]

Hey all, long time lurker, first time poster.
I am very new to cars, always been a motorcycle guy. But I've been working on a friends 2006 Audi A4 Cabriolet (1.8T). It was sitting for about 5 years and we are getting it running for fun, replaced a whole bunch of parts (mostly electronic, due to flooding).

Now I only have one code: P1111/17519: Oxygen sensor control; Bank 1: System too lean
It starts and runs fine. Idle is a little rough, and it feels like it might be lacking some power, but nothing that concerning. I have looked all over for vacuum leaks but have not had any luck.

I took some readings running from idle->6K->idle, but honestly feel like I'm in over my head, ended up more confused than before:
800 rpm (14:08:00)

1.53 g/s Mass Air Flow (G70)
9.0 % Adaptation (Idle) Bank 1 Sensor 1
-17.2 % Adaptation (Partial) Bank 1 Sensor 1
25.0 % Lambda Control Bank 1 Sensor 1

6000 rpm (14:09:46)

29.61 g/s Mass Air Flow (G70)
9.0 % Adaptation (Idle) Bank 1 Sensor 1
-17.2 % Adaptation (Partial) Bank 1 Sensor 1
7.0 % Lambda Control Bank 1 Sensor 1

6000 rpm (14:09:51)

28.86 g/s Mass Air Flow (G70)
9.0 % Adaptation (Idle) Bank 1 Sensor 1
-17.2 % Adaptation (Partial) Bank 1 Sensor 1
-9.4 % Lambda Control Bank 1 Sensor 1

800 rpm (14:10:19)

1.42 g/s Mass Air Flow (G70)
9.0 % Adaptation (Idle) Bank 1 Sensor 1
-17.2 % Adaptation (Partial) Bank 1 Sensor 1
25.0 % Lambda Control Bank 1 Sensor 1

Questions:
1) Any initial impressions based on the reading?
2) MAF seems fine at idle, but about 100 g/s too low at 6K. So I'm guessing the sensor needs to be replaced? Would it explain the other values?
3) I understand why idle trim doesn't change, but shouldn't partial trim be changing? Trims are taken from about 3-4 hours of driving after being reset.
4) Why would idle and partial trims be flipping so far from positive to negative like that?
5) MVB33 is solidly stuck at 25% (2V) at idle. Originally I thought it was bad, but it drops to about -10% at 6K, so I'm guessing that's not my problem.

THANK YOU for any help and sorry in advance for being such an amateur.

[xRenesis]

Check your fuel pressure regulator lines. Or stuck fpr. You can get maf/electrical cleaner spray you can try too after taking the sensor out or filter off depending on the setup


I would also add, if that maf is parked revving, you won't see full g/s if the turbo isnt building boost

[Jayz691]

Yeah, these cars are load based, so not load(reving, etc) wont build boost. Or if your on the highway cruising, your airflow will be a lot lower than if your on the gas(TB open).
Your idle LTFT's(9%) and correction(25%) show that at idle, ecu is really adding fuel. That's correction at 25% is maxed out.
So either lacking fuel, or a massive air leak.

Sent from my LM-V600 using Audizine Forum mobile app

[AliBaba.BoomBap]

Thanks for the help. Wasn't quite sure how to check fuel lines. But went looking for the MAF. The sleeving at the top of the harness had a hole in it - the terminals were all corroded. I guess you need a special tool to test an MAF sensor, so I just threw a new one on and it got rid of the code. Repaired the wiring too. I probably accidently tore it while I was working on other things. Thanks for the help!