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Discussion Starter #1
I have a 2005 Passat 4 motion wagon, 1.8T.

Was throwing the P0171 code, figured vacuum leak somewhere in the miles of hoses there is a leak somewhere, duh. Intake and MAF were fine (found some nice array of leaves, sticks and twigs in the filter box). Still couldn't find any issues, reset the code still came back.

Finally found the issue, now I just need to figure out the part and I can't find my Bentley book, so here I am.

p0171.jpg

The part circled in yellow is the issue, looks like a hard plastic thing that goes into hoses on either end, sorry for the technical terms, been up since 4 and want to sleep lol.

I think it's a check valve, at least that is about all I can find that looks similar online.

Did I guess right or is there another answer?
 

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You got it. That is a check valve. Note the flow direction so you can put a replacement in the same orientation. You'll need a couple screw-type hose clamps to replace the one-time-use clamps.
 

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Are you getting any misfires or slightly "off" idling?

It's the check valve that runs from the little port at the back of the valve cover and down to the bleeder valve. In previous years, it did not exist. In fact the 034 motorsports kit does away with it. You can plug both hose ends and get by until you get a replacement.

Mine came apart on my 04 and did not throw any codes. Also check the hose coming off the intake manifold that leads under to the aforementioned bleeder valve. Sometimes that valve will blow through and cause a lean condition. Pinch that lime shut to see if any running behavior changes.
 

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Discussion Starter #4
I'm sure this is the issue for the P0171 code, however, there could definitely be others. This specific one was pretty simple to deduce (even for me, lol) once I finally found it. The plastic section that goes into the hose snapped off, so that section is still in the hose and the rest of the valve is intact. As long as they are "lined up" for lack of a better word, it idles fine but the CEL will come back on. I can just separate them and you can hear the vacuum hiss and the idle will be off. I will definitely look underneath there when I replace it for anything else as I'm pretty sure everything is all original (I bought the car used last year).

This thing seems to have tons of little air hoses all over the place, something I'm not used to, most of my experience is on Honda's and old Ford trucks with carbs.
 

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This thing seems to have tons of little air hoses all over the place, something I'm not used to, most of my experience is on Honda's and old Ford trucks with carbs.
(GRIN) Yeah, it's "not your fathers Oldsmobile." Combination of turbocharger, emissions requirements, and German over-engineering. There are those (not me) who go in and rip out all that nasty stuff (SAIP, PCV system, etc.) in search of a cleaner look. Search "shaved engine bay."
 

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I also like how the prices on theses things go from $6-56, WTF
You can get good aftermarket check valves very cheaply. Agree the VW one is stupid expensive. As for the rest of the under hood "clutter" there are few alternate sources, and with currency exchange rates, shipping, etc, German parts aren't cheap.

Come to think of it, these cars "aren't your fathers VW" either. My old air-cooled Beetle, I could fix anything with a 13mm wrench and some duct tape - MAYBE some tin snips. Not any more!
 
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