What is this sensor? and what's the effect of its being disconnected?

[visionguru]

The one marked No. 19.
When I was removing the air cleaner box, I was surprised to find that the vacuum hose connected to No.19 was disconnected. Now, I connected the vacuum hose, and the car seems running a lot better especially the idle quality at a cold start.
Can anyone enlighen me what the effect of this sensor is?
Maybe it's just a coincidence, but if my rough cold start idle is related to this, I might need not to try to figure it out anymore.
Thanks.

[A20A1]

"Air bleed valve"
Tts a metal leaf spring that shuts when cold and opens when hot to control the hot air intake diaphragm #15.

[Tailfin]

The design of that is to maintain a constant intake air temperature; however, I've found that it's necessary in cold weather during warming up in order to keep the carburetor from icing up a bit, despite a coolant line to it. It could be helping it run better because of that, or just making the fuel-air mixture more favorable if you were running a little lean.

[visionguru]

There are TWO air bleeder valves in the air cleaner box. According to the manual, the one I refered to is Air Bleeder Valve B, which is connected to Vacuum Hose #33. (#19 in the parts picture.)
The one related to Intake Air Controll Diaphragm is called Air Bleeder Valve A, which is connected to Vacuum Hose #8. (#20 in the parts picture.) The Hot air door seems working correctly. (it stayed up for about 5min, and then close).
After examining the vacuum diagram, I still could not figure out the effect of Air Bleeder Valve B at Hose #33 being disconnected. EGR?

[visionguru]

Sorry, my error.

After close examination, the vacuum hose is connected to an open hole inside the air cleaner.