That is not the vacuum booster, but a vacuum transducer. It reduces the vacuum for the transmission depending on turbo boost.
Is the line disconnected and open? or blocked off? Otherwise the ALDA would not get the turbo boost needed to increase the fuel.
Reconnecting the line can have several effects, depending on how the vacuum lines are connected right now and whether the vacuum transducer is still working. You need a vacuum gauge and an hand pump (one which can build vacuum and pressure) to test the transducer and the rest of the vacuum system.
MB used the transducer to smooth out the vacuum signal to the transmission, so that shifts would be less clunky. If it works, it works well.
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