What is the purpose of the vacuum line going to the air filter box?

I found mine to be disconnected or popped off and am curious. Found it when I was troubleshooting an engine that would stumble but not start, and when looking over the vacuum lines, I noticed the asv was stuck closed!!

Needless to say, lots of soot when the engine finally started. I wonder if it would be possible to fill the cylinders with enough fuel to hydrolock if someone kept cranking lots of times?

Hi, if you trace that hose you will find that it connects to 3 vacuum solenoids, serving as the relief for vacuum when the valves are cycled. It is important to keep it connected to keep the valves and intake from ingesting dirt.

Several of us have found if its not connected engine won't run worth a ...

dieselherb
I have never heard of that being a problem unless it was left off for an extended time and sucked dirt into the system.
The hole that the line goes too on the air cleaner box is very small. I think it might be some form of restriction meant to slow down the vacuum system.
I have that hose off on both of my TDIs with a plastic gas fuel filter acting as an air filter. There is almost no restriction. Yes, I did plug the hole in the air cleaner
Gil