Search feature to the resuce ! found this thread with the exact same question : 190D 2.5 Vacuum line

Its a vent line to the vacuum system !

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1987 190D 2.5 Non-Turbo , automatic
Currently fixing : diagnosing vacuum functions,
, fuel leak at injectors, Dash Re-covering , speaker replacement with aftermarket amp and new wiring, generic keyless entry system .

Future projects :, antenna , Transmission modulator pressure adjustment or replacement... more to come...

Fixed : Windows, Ground wiring cleaning, random transmission kick-downs.