Hi all, I have a 2001 A4 1.8T with a lean (P0171) condition and I'm trying to find if it's a vacuum leak. I cleaned the MAF, reset the CEL, and it came back on after 20 miles. I realize I may still have to replace the MAF, but want to make sure I don't have a vacuum leak first. I can't visibly see a leak, but while poking around I noticed a couple things that I want to ask if they are normal. I removed a hose from the intake system and blew in it, thinking I should not be able to. But I clearly can blow air into it and after poking around some more I was able to see where it was coming from. Now I'm not sure what these components are called, so I try show you with pictures. So I blow like this:



...and air comes out from under this thing here. I can get my hand underneath and feel an opening. I wonder if there is a hose that should be connected here?



Here's a picture from underneath (using a mirror). I can't seem to make out the part number.



I hope you can understand what I'm trying to explain. It this supposed to be open to the atmosphere or should there be a hose attached? When I plug it with my finger while the (warm) engine is running,nothing seems to happen.

Other symptoms I'm having is some knocking at idle when the engine is cold. This goes away when it warms up. I'm hoping this might be a result of the lean mixture causing a knock.

Thanks for any help!
-Wilder
Pacifica, CA

 

Find a smoke tester and pressure test the intake, if you don't have one have the dealer do it for just labor time. If ANY smoke comes out you should be able to find it. As for air blowing out of the intake that would be more of a boost leak than a lean concern, but i doubt its anything to worry about.