Intake Control Solenoid on a 97 Honda Accord VTI-S, what's it for?

I ask because I'm DIY installing an after market performance air filter with tube and realized there isn't a place to plug the vacuum line that comes from the Intake Control Solenoid valve on the new air filter tube.

Do I just cap it and close it out?

On the stock air intake tube it is connected to a box and it seems to control a diaphragm inside that box... I'm not sure what it is for?