Idle Air Control / Air valve
 

Hi.
I have a Mazda 323 F 1990, with the SOHC engine (103 hp).
I am troubleshooting a rough idle. Its not that bad, perfectly driveable, but the idle is little low
when the engine is warm and it vibrates because of this at stop lights.
When the car is started cold the idle is quite high, maybe 1500 rpm. I don't know if that is normal.

So I've come to the part referred as "air valve" in the service manual. This is the one that sits on the side of the throttle body (under the throttle body on the DOHC engines).
The way to test it in the manual is to cool it below 0 degrees C, and then look at the spring loaded valve inside while warming it up with a dryer. If its working, it should move.
But! It doesn't say how much it should move! I figure it should move a cm? Mine moves maybe 1-2 mm.

I've been trying to clean it out with some lubricant spray and compressed air, but it still barely moves when warming it up.
Should I replace it?

Another question, the gasket between this air valve and the throttle body seems to be tough to put back because it has expanded since I removed it. Are there any good ideas how to shrink it back when installing? Putting in some solvent or freezing it?