Based on the Z32 vacuum diagram wiki page, it looks like the vacuum line that runs to the AIV solenoid. It's completely uncapped & has been this way for some time now
Is this okay to be left uncapped? I didn't have any vacuum caps otherwise I would have thrown one on but I also haven't noticed any issues such as a vacuum leak.
Follow Ups
Uncapped vacuum nipple on passenger side accordion - nissubaru16:17:51 09/24/18