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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