It's a somewhat complicated vacuum system. Do a search for OM602 vacuum diagram.

A number of us have found that simplifying the vacuum system removes some variables that can be troublesome. See the PDF of essential vacuum routing here: https://www.peachparts.com/shopforum/diesel-discussion/420846-1993-300sd-egr-delete-wastegate-function.html

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 179k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 77k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife