940 1995 Non-Turbo

I'm still trying to resolve my idling problem. Have been told to check on the air cond vac line. Is the air cond vac line at the back of the throttle body above the hose (big one) that leads to the IAC?

If that is the air cond vac line, I'm still trying to figure out why it is plugged at the other end of the line. This vac line runs from the intake through the firewall and to the drivers footwell (mine's a right hand drive) and is clipped on along with some other wires. But it is plugged and not connected to any device! There is a white colored cone shape plug stuck on to the open end of the line and it seems to me that it was put there on purpose and not like the line had came on loose from its fittings.

Can anyone tell me why this is so and why should it affect idling since it is plugged anyway?

Thanks for the information in advance.
Still working at my idling issue. Hope to find an answer fast.

Laozong