I have found a loose vacuum line that is related to the unknown components below. Looking at front of the engine on the drivers side: The left ? is the loose vacuum line, the center ? is an unknown solenoid valve (or looks to be), and the right ? is a vacuum actuator that rotates a shaft in the intake.

Any help is appreciated. I need to know where the supply line connects and what this system's function would be?

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold

The vacuum solenoid operates the intake manifold resonance flap.

https://en.wikipedia.org/wiki/Variable-length_intake_manifold

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98 Dodge-Cummins pickup (137K)
13 GLK250 (157k)
06 E320CDI (341K)
16 C300 (89K)
82 300GD Gelaendewagen (54K)

Thanks for the info. The vacuum line hooks underneath the intake manifold and is pretty difficult to access. For now I plugged the hole and teed the vacuum line into the EGR Intake Pressure switch sensor line. Not sure if it works or not. At least the engine idles better with the vacuum leak stopped.

__________________
1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold