Thanks Jeffrey, appreciate the info. So the Shop Manual indicated (step 3) to set idling speed to 450-500 RPM by adjusting the stop screw on the throttle lever. Then (step 4) to turn the idling screw Left or Right, until your gauge reaches the highest Vacuum, which should be between 17-21. I found that turning to the right, the engine started to stumble, but turning it to the left (counter clockwise) raised the vacuum.
