AOS Question

[bradshjr]

When I read that an AOS "goes out" or needs replacing, I'm somewhat confused. What exactly goes bad on it. I can understand the bellows tube cracking, but since there are no moving parts (that I know of) and no mechanical devices inside, what makes them go bad. Would not a thorough cleaning and a replacement of the bellows tube restore it to like new condition?
I'm sure a lack of understanding is my problem....

I'm having bad idle control problems. I've cleaned the throttle body, MAF, and idle air control valve, but it still hunts for proper idle and frequently dies when the clutch is pushed in. I have to feather it down to 1000 rpm or so before applying the clutch to keep it from dying, and even this doesn't work every time. I figure the AOS is next on the list, but I need to understand what can be bad on it. Thanks