No gasket needed.
Its got a brown connector/plug on it at the rear of plenum chamber. (Near the hose that runs to the brake booster)
It may be faulty, or it may not be plugged on properly or it may have a broken wire between the ecu and valve.
If you measure the connector with the ignition on, it should have +12V on one of the wires, and the other wire runs to pin 4 on the ecu, the ecu pulses the valve to ground to control how far it stays open.
You could even, connect a 12V battery to the aac valve when you get it off the vehicle and see if it opens with power applied. (Its a solonoid so the plunger will pull in when you connect 12V to it)
I would check the valve first before just replacing it.