If the vacuum valve that is attached to the ignition switch is going bad what type of symptoms would you expect to have and would it have an effect on the IP shutoff/or not shutting off and would it have an effect on the door locking system?

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84 300D, 82 Volvo 244Gl Diesel

In my case the switch started leaking vacuum and would result in the gradual shutdown of the engine as enough vacuum built up in the shut off valve to shut down the fuel rack. I do not think they can fail the other way looking at how it is built. Probably designed as a fail safe.

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It would result in not shutting down or taking a long time to shut down. I would try plugging a mity vac into the shut-off valve on the IP and then start the car and give is a pump or two and see if the car shuts down quickly or if it stumbles to a stop. You shouldn't have to give it more than one or two pumps. If you have to give it more or it stumbles to a stop then the valve on the IP is bad. If it's works fine then you may have a bad ignition shut-off valve.

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A vacuum leak anywhere can affect just about any other vacuum consumer.

If this is the case, and the valve requires vacuum only to shut the engine down, what could be the cause of the engine not starting?

In my case, after several months of having to shut the engine down manually, it did shut down by the key, but now won't start, that's more likely to be the valve at the ignition switch? Or, is it possible for that valve to fail in the closed position?

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Resurrected Nov 2010 - 79 240(SD) with 83 617 engine and 4 speed manual, 2.88 rear and 2.5" straight pipe unknown mileage (Salmon)
83 240D parting out
96 Dodge Cummins 5 sp 4X4 long bed - 310k

http://flickr.com/photos/11103112@N03/

You might need to adjust the shut off valve linkage. It sounds as though the valve actuated and now is not resetting.

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Dave
1983 300D Daily Driver

I went out this morning and pulled the vacuum lines off the ignition switch and plugged them together. The car started right up, unfortunately, when I put them back on the switch it started right up?

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Resurrected Nov 2010 - 79 240(SD) with 83 617 engine and 4 speed manual, 2.88 rear and 2.5" straight pipe unknown mileage (Salmon)
83 240D parting out
96 Dodge Cummins 5 sp 4X4 long bed - 310k

http://flickr.com/photos/11103112@N03/