Gday guys,
I wonder if any of you would know whats going on with my car.
When i have the tube connected the engine's rpm fluctuates when idle.
When i block the pipe (pink circle) the idle is fine, except when i turn the ac on it'll cut out or idle VERY low

This leads me to believe that the thing (plz tell me what it is) (red circle) has something to do with this.

Im pretty sure it has nothing to do with the idle valve cos it idles fine when the pipe is blocked. Except if im sitting in traffic for ages
its like the engine is gasping for air, and starts idling low again.

I suspect the problem is the thing (red circle) which is stuffing up and not allowing air to by-pass the butterfly valve when
sitting in traffic/ having ac on.

Much grattitude will be given to whoever can help me. cheers guys.

one last thing, is the thing (yellow circle) a catch can of some sort?? or what is it? (hope the pic works)