shut off valve engages but it wont rotate the last degree to fully shut off engine. it only slows the Idle. diaphragm seems to be OK any ideas

Check by putting vacuum directly to the valve? Sounds like a vacuum leak.

Please post only once, and delete your other two posts.

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Gone to the dark side

- Jeff

Could the unit at the rear of the IP be at fault?

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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.