mishar

At which point of that "blip" you hear it? While the rpm is rising or after it?

nathanwind

As soon as I get on the gas and it starts to rev, I hear the sound....RPMs seem to catch up and peak just a split second later.

If I feather the gas and idle up slowly I do not hear the sound.

mishar

I've just checked and got exactly the same. Since I don't have any codes (fingers crossed ) I think it is normal.

dvs_dave

Pull the electrical connector off the MAF and run the engine. It'll still run, but default to a safe base map. See what the O2 sensor readings do under these conditions. If still too lean then it's unlikeky the MAF and assuming the electrics are ok it's either a vacuum leak or fuel delivery issue.

nathanwind

Ok quick update on the latest. I actually received a "Free Check Engine Light Diagnostic" flyer from my local Audi DEALER. So, figured what the heck....why not bring it to them and see what they find.

Spent the better part of 2-1/2 hours sitting there this morning (yikes). They came out to tell me that I had a Crankcase Valve leak, which was causing my CEL - and that someone had replaced it with a cheap knockoff replacement part. I let them finish, and then informed them that I purchased it directly from their Parts Department 6 days ago. Queue 'deer in headlights' look. At this point, they got the tech on the phone and I was able to go down and speak with him face-to-face.

I informed him as well that the PCV/Crankcase Valve came directly from them, and it was a straight-forward swap (that I did) with literally 2 hose clamps. He pointed out to me that it was definitely purging air constantly (which it was while we were there in the bay), and that was not normal - that it *should* self-regulate and open/close periodically based on a specific pressure once it was at that level. You could literally hear the "new" valve running, and when you put your hand on it you could also feel the vibration. Both noise & vibration were constant.

His conclusion (and written up on the paperwork) was that the vacuum leak was the PCV/Crankcase Valve was the culprit - essentially letting excessive air into the system, therefore causing the "too lean" codes (he pulled the same P2195/P2197 codes I had found, and showed them to me).

Trusting his judgement - and the statement that the valve was faulty - I went to speak to the Parts Dept about the findings. They pulled up my paperwork, and agreed to swap it out. I needed to head back home first in order to put the "old" one back on.

Doing so, when I put the old one back on (note: while I wasn't 100% sure the original PCV Valve was faulty, there had been some prior "humming" coming from it months ago as alluded to in my earlier posts - so thought it couldn't hurt to swap it out for a new genuine one). After the swap back to the old one, admittedly both the constant noise & vibration ceased and it quieted back down.

Returned to the dealership under the assumption the new/genuine Crankcase Valve was faulty, and they gave me a new one and I was on my way. Got home, swapped the "2nd" new one in....and it did the SAME exact thing - constant purging (which you can hear as a low hum) and you can even feel it vibrate.

So at this point, I suppose the thing to do would be call upon the "masses" to take a look at their PCV/Crankcase Valve - and let me know if yours operates in the fashion that both of the "new" ones that I've tried are. IF that is normal for the rest of you, then I'll chalk it up to poor diagnostics by Audi. HOWEVER, if no one else has the constant air purge/slight vibration through the PCV valve at temp....possibly a bad "batch" of valves from Audi? Seems unlikely - but I suppose you never know.

Attached is a pic of the valve at the top of the motor, you'll see my finger in the photo - if you "close" the opening on the valve shown right in front of my finger (by just putting your finger over it) the noise/vibration does go away. Again, my old one (even when put back on the car) did NOT have the noise/vibration when put back on the vehicle and at operating temp.

dvs_dave

Mine has always had a constant low hum and corresponding vibration at idle and I don't have any codes or CEL. As far as I'm concerned this is normal behavior.

nathanwind

Thanks Dave! Tells me that the old one wasn't functioning properly. However, also tells me that Audi techs don't know what they are doing .

Back to the drawing board. Going to pull the MAF connector as you recommended above. I did it earlier, but immediately threw a TON of other codes (which I supposed I should have expected) so I panicked and cleared everything. I'll give it another run leaving the "other" codes in place to see if the lean codes come back.

nathanwind

Ran it with the MAF disconnected. Same Lean P2195/2197 codes came back. It seems like that rules out a faulty MAF as a possible suspect, correct?

Next attempt: dropped in a bottle of BG 44K Injection Cleaner, going to run it for a tank and see what happens. I know it's not the same as pulling the rail and a "proper" injector service, but figured I'd start with the less intrusive option first.

dvs_dave

I would seem that the MAF is fine given the lean codes remained. So that narrows it down to vacuum leak or fuel delivery issue.

The vacuum system has a leak detection system and as you have no codes for that, I'd focus on the fuel system. Are your fuel pumps working ok? Fuel filter clogged?

Is the car down on power? How does it perform at WOT and high revs? Is it sluggish at the top of the rev range?

nathanwind

Based on the couple years I've had the A8, no does not seem to be down on power at all at any point - high revs or otherwise. I may tap a fuel pressure gauge off the rail, run it under the hood, tape it to the windscreen, and give it a test drive to see if there are any signs of fuel pressure issues. What's expected pressure range, 35-40psi?