Regeneration valve, better know as a purge valve. Such a valve didn't get used until EFI systems LH and HFM.

The purging of the charcoal canister did have a vacuum operated valve in the 380s. The cannister was near the radiator on the drivers side and had a dashpot type valve that allowed air to be pulled over the fuel soaked charcoal during part throttle accelerations. To test plug the line from the valve to the intake and verify that the valve holds vacuum.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician