My 85 300D has the same surging problems occasionally while idling. The tach doesn't move but the oil pressure needle will move up and down slightly in time with the noise. Will adjusting the rack dampener fix this? If I raise the idle with the pedal ever so slightly it clears it up and the wobbling that comes with it.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo