Missing Vacuum cap? PO171, high fuel trim, ckg vac hoses

[CarCapers]

2008 non-turbo 2.4 s40, P0171 code triggered while at idle, just 3 minutes after starting and had fuel trim of 23%

When looking for damaged, cracked, missing vacuum lines I noticed this incongruously clean and shiny stub north of the oil filter (see photos) when facing the engine, looking at the passenger side front quarter, looking down and slightly at an angle. Specifically, if the oil filter cap is center of clock, this horizontal stub is at 11, and pointing to front of car.

Really looks like something used to be covering the metal stub because it doesn't have the same dark patina of oily dust as all around it. Could this stub be connected to the vacuum network? Should there be a cap or tube on the end of this stub? I have spent time going through the Haynes book but not sure what system this stub is contiguous with so it's a needle in a haystack sort of investigation.

[theWIFES_S70]

I drive a 2007 non-turbo S40 and that hole is similarly clean. Your vacuum leak is coming from somewhere else. Maybe the hard lines that snake over the right side of the engine? Good luck tracking it down, it sounds like a pain...

[kallekula]

Buy a cheap smoke machine