yuiou

Hi,

New member with a 2001 S8. This is my first Audi, I'm usually a BMW guy but the right S8 came along and I had to pull the trigger.

I have a few codes on my car:
P0101 - Mass Air Flow (MAF) Sensor Performance
P0171 - Fuel Trim System Lean Bank 1
P0174 - Fuel Trim System Lean Bank 2

Wondering if others have had these, and if so what was the solution?
Maybe an obvious thing to look for on these cars?

I've read that it could be vacuum lines, maf sensor, O2 sensors, loose intake manifold bolts...



Any experience/guidance is appreciated.

Thanks

silverd2

Those is exactly the set* of codes for a large vacuum leak (sucking in un-metered after the MAF)...maybe even the large intake tube from MAF housing to the throttle body unseated(?).

Start looking with the large intake tube, then all visible vacuum hoses.

* If was just one of those codes, you'd be looking at other possible causes...fuel pressure, MAF bad, O2 sensors, etc..

That set says vacuum leak.

yuiou

Thanks.

I'll pull off the cover and chase all the lines.

yuiou

Update:

Replaced all vacuum hoses as per:
audipages 40 Valve Vacuum Hose Replacement

Cleared the codes, and the following ones came back after 15 min:
P0171 - Fuel Trim System Lean Bank 1
P0174 - Fuel Trim System Lean Bank 2

Is the MAF the next logical part to replace? Is there a was to test it?

Thanks.

BrianC72gt

The MAF is in the airbox. Double check that the elbow to the throttle is fully seated...give it the courtesy of a reach around.

There is a thing on top toward the back of the engine...It looks like a black flying saucer. That is your Positive Crankcase Ventilation valve. It gets gunked up FULL of crap - much like me - remove it, wash in hot soapy water from every orifice. Run hot water through it until all the crap stops coming out. Hop it back on there. If it gets stuck partially open it will constantly suck vapors and oil mist from the engine.

Cheap replacement ones are crap and quack like ducks. I kid you not. OEM replacement is spendy. Another poster actually disassembled his to clean it...show off. I would likely break mine in the process. It will cost you nothing but a little time and give you a better view of the little hoses underneath it by the back of the engine. It will also extend the lifespan of that bit indefinitely.

yuiou

Update.

Cleaned PCV and MAF. Codes came back.

Replaced MAF. No more codes.

Hopefully this helps someone in the future.