Air Box Vacuum hose

So I'm pretty noob to the forums, but I have been having a vibration at idle in my 06 taco, 4.0L v6. So this weekend I cleaned the MAF and the throttle body(neither were super dirty). But during cleaning i realised I disconnected a very small vacuum line on the back of the air box. Super small it doesnt even have a clamp on it, my main question is... what does this go to? Because i had left it disconnected for a half a day and drove about 10 and felt nothing and no CEL. Idle actually felt smoother. It obviously needs clean air in it so i may take my compressor and blow out the little hole it plugs onto just to make sure nothing is hindering it. But yeah what do u guys think? Smoother idle with it unplugged from air box + no codes from it so whats it for? Thanks