This is not the way it works on our 190E. The hose goes to the breather side of the pcv orifice, so it would be unlikely to detect much vacuum there unless there is a problem with the engine. The hose simply provides a pathway for fuel if the regulator diaphram ruptures - hopefully back to the air cleaner.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7