Lean On Bank 1

[ZipMeUpJ]

I've been chasing down the solution for a P0171 lean on bank one code, and am interested in what you guys think about the symptoms.

Post from another thread recently:

So I took mt car to a local audi tech and had them run a boost leak test and a smoke test to check for vac leaks. The only thing they came up with was that my n80 was stuck open and the reason for my Evap leak. Ok.

I purchase a branch new n80 form the dealer (b7 version), install and car runs full boost for 20 minutes. P0171 is back (lean on bank 1).


I ran a couple tests myself again to narrow this down:

At idle
Vac 29.9Hg
Maf 2-2.5g
STFT - 7 to 6
LTFT still high at 22.0


Redline in 2nd gear reaching 60mph
Boost 5lbs
MAF read 60gs on several attempts
A few times I reached the 100s.
Several weeks ago I ran the same redline test and saw 120gs


Steady at 60mph
MAF reads 20gs.



It definitely has to be my Maf correct?

Just to the present: I still think I have a leak somewhere. MY LTFT climbed back to 22.7, although a lot slower, after a day of fiddling with it and staying out of boost. The battery had died after my last fix-it session, so I took the chance to see how the car would react if I babied it instead.

When the car is not in limp mode and I can hit full boost, I was seeing ~120Gs from the MAF around redline, and in the above post when I was seeing half I can assume is because I was then in limp mode.

As a kicker, the mechanic did point me to a very new and dirty layer of oil on/around the plastic T, near the breather elbow, under the intake manifold. I replaced the breather elbow and T iirc about 2 years ago.


I am not sure if my P0171 bug will be more likely related to a boost/intake leak or with this newly discovered dirty area under the manifold?

[old guy]

Although you mentioned that your mechanic performed a boost leak test your symptoms point to a false air condition. You stated that your vacuum at idle was 29.9 inHg. An obvious misprint. Did you mean to state 19.9?

As you know your 22% LTFT is extremely high. Thus the P0171 and limp mode. You also mentioned that your MAF g/s at idle was 2→2.5. Although in spec it is at the very low end.

Try this simple test. Monitor your MAF reading at idle. While at idle clamp off each vacuum line connected to the intake manifold one at a time and see if you notice any difference in the MAF flow rate. Also try wiggling the hoses as well as the TIP while monitoring the flow rate. If you notice any significant difference start checking further down the particular hose until you find the defective component.

[MikTip]

The 10,000 various hoses on the B6 1.8t are a constant source of various boost leaks/ vacuum leaks/ leaks...

Many you cannot see, and often take sometime to locate...

Ask me how I know!



Plus, you fix one...another one will occur...BTDT!