the engine doesn't start screaming. Idle just goes up a bit when I turn the ignition key off.
Anyone know the answer? If vacuum is applied directly to the valve and the car does not turn off does this indicate that the valve itself is bad?

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.