03 5.8 Plenum air fitting Q

Some soon to be dead chipmunks have been at work chewing up some wires and other rubber bits on the engine of our Durango. On the right side of the plenum there is a fitting for an air hose that I think just has a rubber vacuum cap on it and I just need someone to verify this. If there is supposed to be a hose where does the other end go. I just discovered it tonight and fortunately no wires are chewed in two, just some small amounts of insulation chewed off. This hose bung just had the section of rubber left , the end of the bung was open. Surprisingly, I couldn't tell any difference in the driveability. Just smelled something weird when we walked by the front of the truck.

Thanks
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