Honda Civic 96 VTi : Pipe connection from the Part connected to IACV

[FFAROOQ]

Hi All,

Please see the attached picture.
My Car issue is unexpected behaviour of the Car during idling.
I have cleaned the IACV valve. Reset the ECU twice.
But it did not helped.
While troubleshooting I found a small pipe whose one end is blocked with a Nut (Bolt) & other end is directly connected to the part which is exactly behind IACV & Throttle Body structure. While the Car was running & I removed the Bolt & placed my finger, I can sense the Air being sucked in & while the Finger was not blocking it, Car Engine REVs were excellent & as soon as I put the Nut back, Engine REVs became very low.
Please let me know, where the other end of this pipe will go.

Thanks in advance.