The monovalve controls the flow of coolant into the heater core. When the valve is fully open, full flow goes to the core and you get maximum heat. The monovalve is the first culprit when you don't get any heat. I just bought a kit on e-bay for $20.00. They are on there every week.

The monovalve has nothing whatsoever to do with the vehicle taking five seconds to shut down. This is likely related to the vacuum shutoff on the back of the IP. See if you can shut the engine down with the Mityvac. If it shuts right down, then, your problem is in the supply of vacuum to the shutoff. You might have low vacuum in the system, or the key switch is not functioning properly. Track it down with a vacuum gauge.