The Dawes device, when cranked down, is capable of ~ completely blocking boost pressure to the wastegate, thereby raising boost to the engine and ALDA . Take yours apart and clean it and check the ball seal. There is a very small (and I mean nearly microscopic) vent hole in the side of the device that you're supposed to clean with a FINE wire, also. Check banjo fitting for boost line to ALDA as the fuel enrichment works in synergy with boost in sort of a feedback like circuit.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)