If it is a rotary idle control valve, it is easy to check for smooth operation. The angle of the shaft and thus the size of the port opening should vary smoothly and consistently as you vary the current to the terminals. Any stickiness in action, and you should clean it in solvent, using wood-stemmed cotton swabs to work off any tougher deposits. I used rubbing alcohol.

Not much else can go wrong with it, but lots of opportunities for air-path leaks elsewhere in the rubber plumbing.

Steve