Thanks everyone for the replies. I’m just advising from a far on this one. Waiting for my buddy to have time to mess with it. From what I’m hearing from him about when it happens I’m putting my bet on waste gate issue.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"