No, it wouldn't bubble with soapy water. The soapy water would be sucked in. The IAC makes a hissing noise when the throttle is adjusted properly. Not talking about pinching a hose either... There should be an slightly audible noise comming from the hose connecting the IAC to the intake manifold. It just is always there. When you cover the hose it goes away.

The IAC also makes an electrical buzz when it's sitting perfectly at 1/4 open, on it's spring. That varries with temperature and conditions though.

 

I was having idle issues and was trying to adjust my idle just the other day, and I heard this hissing sound. Then when I fixed the problem and the hissing sound was still there, I though it must just be the IAC. Guess I was right.
thanks