I have same problem on 2001 2.3L
My vacuum hose runs from driver side top at back of engine goes straight down to? It's a 1/2" OD rubber hose and it's very soft, so it colapses to almost and makes idle run up and down. If I use my fingers to bring to hose back to its round position it gets better suction and idle smoothes out.
The thing is, I don't know where it goes to! I can see the first 18 inches or so between engine and fire wall and that it.
I really want to change it but don't know what it is.