You probably have a hole in the PCV tube elbow. Find the valve (in the middle of the passenger valve cover) and follow the tube to the back of the intake and feel the elbow. It may help to have the engine running so if you put your finger over the hole you can feel the vacuum. If it is the tube then first I would find a different mechanic b/c if he cant find a simple vac leak then he dont need to be turning wrenches, second go to the dealer and buy the tube and replace it. Shouldnt be more than 50 bucks.