If I understand correctly, you plugged the one line from the pump. Did you
try plugging just one of the gray lines, then the other? I think that check
valve is a one-way flow.
Like TG says, most likely a door lock element gone bad. Or the vac hose
running to the drivers door, at the hinge. The easiest place to check that
stuff is in the passengers foot well, under the carpet. After unsnapping the
carpet, remove the couple of screws that hold the cover plate. Under that is
where all the connections to the doors, fuel flap, trunk lid, etc. are
located. Each element has a lock side and an unlock side. In other words,
vacuum must be applied to one side of the element to lock the door and
vacuum must be applied to the other side of the element to unlock the door.
You will need a hand held vacuum pump (thirty bucks at the local parts
store), a couple of golf tees and some time. Unplug each element's pair of
lines. You will be able to tell the pairs of vac lines by their color/stripe
code. Apply vacuum to each line. That will lock and unlock each door. If (or
when) you find an element that doesn't respond, plug that line. Then start
the car and see if that was the only leak. If it was, the car should shut
off. Depending upon which element is bad will determine the complexity of
your next lesson in the art of car care.
In the back yard, under the oak.