As long as the system is sealed and you are at idle than you should still have a steady vacuum gauge reading of 17-21. Does the vehicle idle rough? Is the CEL on? If I were you I would grab a can of 2+2 gum cutter and with the engine running spray it around all vacuum lines and intake gaskets. If you do have a vacuum leak it should become apparent with this fore the engine idle will fluctuate. Is this a manual trans car? Are you sure the clutch isnt slipping? The restrictor pill only limits boost pressure.