Thanks for replying. My interest in particular is in the plastic box and not the IAC valve itself. When I said muffler I meant something to dampen air noises. It's possible when the IAC is cycling it might make some strange sounds that would be noticeable inside the car. The intake on my Isuzu diesel truck has just such a device, with no throttle in the intake you would hear the wide open intake noises all the time. Cool for short periods in our Stangs but I don't think I would want to listen to it full time! As you noted there is nothing inside it so I have to wonder how necessary it is. Running a hose only would look alot cleaner.