Quick update to this thread (and possibly, another question as well...)

Finally found that the fuel banks 1 and 2 lean issue in my case is due to "unmetered air" entering the system. The vacuum lines are all good but, through N80, there seems to be a leak in the hose / section around the leak detection pump (Haven't opened the rear wheel well yet to fix it). Blocked the hose that goes to intake from N80 and the lean issues are gone.

However, I still get :

17549 - Load Calculation Cross Check
P1141 - 35-10 - Implausible Value - Intermittent

Ross-Tech says:

Possible Causes

Mass Air Flow Sensor (G70) OR Manifold Pressure Sensor (G71) faulty
Vacuum Lines faulty

Verified that vacuum holding well in all areas.
Mass Air Flow reads: @680rpm 4.7~5.0g/s settling around 4.8g/s.
That is in spec as per diagnostics procedure. Will be test-driving wot on 2nd to find peak.
Also performed a throttle valve control module adaptation (will do it again after cleaning)

Drove the car today for over 80 miles and readiness still indicates Oxygen Sensor(s): Failed or incomplete.

Would bad O2 sensors cause the 17549 code? How to test the o2 sensors? I tested the heaters and they are fine. What groups/pids etc. to look for with what values for normal operation of o2 sensors?

 

This thread is so old and I keep posting updates. Anyway, I am happy to report that the issue is fixed finally and yes, it is the Mass Air Flow sensor. I know, I know, I can hear you guys say, "I told you so.." (and, I Thank You) but, I couldn't justify spending >$120+ for a part I wasn't sure is broken.

When I checked MBlocks 002 @idle, the old MAF is in spec as per manual. So, I started hunting for other source(s) of malfunction. Isolating the EVAP removed the Banks 1&2 Lean issues. 17549 and 17551 codes continued to exist. Plugged EVAP (N80, see my posts below) back in and ran diagnostic and N80 and Leak detection pump are fine as in "System OK". Test drive and Lean codes came back. Cursed and tried to generate readiness and O2 sensors tests would not perform. Naturally, thought O2s were bad so, tested them in-circuit with oscilloscope and response time / voltages are fine (yes, the electronics background helps :-)).

Decided to road test and log MAF @WOT. Got only 154.xx as max g/s. Still wasn't sure if MAF is bad (as I believed the whole notion of "MAF reading should be approx. horse power x 0.80", to be some sort of pseudo science rather than a tangible spec I could rely on so, dismissed it thus far). But, the persistence of 17549 and 17551 along with [MODE 7 OBDII = pending DTCs] P0106 - Manifold / Barometric Pressure Sensor (G71) / (F96): Implausible Signal, started to give me a strong hint that it could be the MAF. Decided to take a chance and bought an OEM part (RPM Foreign Auto Parts - if you are in Northern NJ is THE place to get Audi parts for excellent prices! Trust me on this). Test drove and logged MBlocks 002 @WOT and it went up to 224 g/s @ 64xx rpm.

For the first time, I couldn't believe my eyes as checking Engine codes read: "No fault Code found"! Then, went ahead and generated readiness code and all tests ran fine without any issues. Got inspection passed and felt like I climbed Mt. Everest!

Putting things back together, I opened the "crankcase breather valve" or PCV valve whatever it is, and cleaned the diaphragm, spring and housing with throttle cleaner spray can and put it back in. Now, there is no "womp womp.." sound anymore!

So, lesson I learned: Bad MAF (upper tolerance bad) confused ECU enough to set improper fuel/air ratios and (don't ask me the details as I am not sure completely) changed the way intake section is functioning. This started to draw air through N80 and the PCV valve (hence the womp womp) and fuel banks 1 and 2 to be lean (perhaps, the added air O2s are seeing could be setting this). Replacing MAF fixed these issues and car now performs well. Perhaps, >117k miles and the fact that I went cheap on air-filter few times could've contributed to MAF failure. Will be using only OEM air filters from now on. I've always used OEM oil and pollen filters anyway (hey! the air I breathe is more important than what the engine breathes. I guess it wants cleaner air as well :-)).

Maybe not required, before replacing the MAF, disconnected the battery (mainly to reset ECU). Plugged everything back, cleared all codes, performed Throttle valve adaptation and then test drove.

I sincerely hope this thread becomes useful to someone who might be having same or similar issue(s). Even if you get a hint or a possible place/point to troubleshoot after reading this "novel", my effort is worth it!

I Thank everyone for your input!

 

its actually refreshing to see you post your findings, so many people come here asking questions then dissapear without even a courtesy update.

 

Thank you and yes, I really do wish others would take a moment of their time to post the fixes because that's what helps others. But, truth be told, many do post their findings, as well as tips & tricks. I've learned so much by reading others' posts, of course, particular to Audi. Next job is Oil Cooler coolant pipe. Already found good amount of posts regarding this so, will be back soon. So, its not so bad. I'd imagine any forum will have drive-bys that never come back. But I love this forum so, I come back often and try to help out with the little knowledge I have. :-)

 

What a great thread and most important to see a resolution! Nice work

 

OH MY GOSH. I have been trying to figure this out for over a YEAR and stumbled upon this today after hours of skimming. My lean codes are quickly followed by MAF codes, and shortly thereafter ESP faults set off causing all sorts of fun transmission shifting issues. I'd been trying to figure this out for MONTHS why they are intertwined somehow. THANKS so much for this!! Now I need to figure out my lean issues because my MAFs have both been replaced! Haha

 

Will this be the case on a 2007 Q7 4.2 as well? Does it have a 'suction jet pump'? Thanks!