Originally Posted by otto huber

With the engine running take the mityvac and run it to the shut off solenoid at the back of the injection pump. If a few pumps on the mityvac shuts the car off then move on down the line and check for leaks. You can also test the ignition shut off valve(this valve is located on the ignition key tumbler). If that valve isn't holding vacuum then you'll need to replace it.