What should vacuum be at the shut off valve?

[petecooke]

My car doesn't stop until I rev up the engine after I turn the car off.

I'm getting 22-23 directly from the vacuum pump.

I've plugged every vacuum line with golf tees except the one going to the ignition shutoff valve.

My vacuum gauge shows 12 when I turn the engine off right at the vacuum shutoff valve..

Is that enough vacuum to turn the engine off?

I wish I had another diesel benz to test this.

Thx

pete