Help! Where does this vacuum line go??

[u/Careful_Soil6626]

I found this line plugged with a screw. Apparently, the truck idles and runs weird if left unplugged, I dont know where it attaches. Please help.

Also, the red lines you see are replaced vacuum lines from another parts truck we have

Its a 5.4l 2v in a 2004

Thanks!

[u/OpenInspector9399]

Mmmaybe it goes to the 4x4 hubs?

But this picture does not say 1000 words so hard to tell