The car is a 1988 300SE. While hunting around the Klima, I noticed a hole almost in the middle of the air filter cover. It's just closer to the windshield than the Mercedes star emblem. The hole has a rubber grommet inset into the hole. If I didn't know better, it looks like the hole old American cars used to put a wing nut on to hold the filter closed. On the MB I have one nut and each if the 4 corners. Then there's a hole with a black rubber hose attached to it. Then there's this hole I'm speaking of that has nothing and is simply a hole with the black rubber grommet.

I did start the car and plug and unplug the hole. I didn't notice any change in the engine.

Thanks to anyone who can tell me what is supposed to be in this hole.

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Thanks,
Ron Brooks