I happened to notice my air cleaner was missing the little round plug near the center (see photo), so I picked one up at PartsShop.

Then I started wondering -- what's the purpose of the plug? I assume it's always supposed to be attached, as dirty air could be sucked in otherwise? Have horrible things happened to my car from this plug being missing (presumably for years?)

Is it an access hole for an adjustment tool or something?

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1992 300E Sedan (Sold)
1999 E320 Wagon (Sold)
1995 E320 Sedan
1995 E320 Wagon