Does the vacum tank act as a delay or softening device so that the air control valve does not act too quickly for the given pressure? Causing the car to be more "stable" at on/off throttle.

:edit:

http://www.hondaautomotiveparts.com/auto/j...ry5=VACUUM+TANK

 

This is an emissions related item.
If you trace the vacuum lines, one goes to the intake manifold, and the other goes to the second air control valve.

 

The vacuum tank holds "nothing"

 

The only time the Vacuum tank is used is when the Air injection system is operating at cold start.

The PCM turns on the air pump control vaccuum solenoid valve when the air pump is running. This allows engine vacuum to flow through the tank, and the check valve and open the Air control valve on the back of the intake manifold.

With the air control valve open, fresh air from the air pump is allowed to flow into the exhaust ports, adding oxygen to the exhaust stream.

Since the car runs rich at cold start, the addition oxygen allows the remaining fuel to burn in the manifold and warm up the catalytic convertor faster. 2 things are acccomplished. The convertor heats up and begins functioning very early in the cold start cycle, and unburned fuel is not allowed out of the tailpipe.

The air control valve has a pretty large diaphragm and needs the stored vaccum in the tank to open quickly when the PCM turns on the air pump control vaccuum solenoid.

It has nothing to do with the idle control system.

 

Thanks Slow, just what I was looking for.