Originally Posted by wstar

Another way you can check for vacuum leaks in the intake tract (PCV hoses, etc, aside from the main intake tubes and throttle bodies) is to spray something volatile like starting fluid nearby the suspected connection with the engine running. If there's a vacuum leak the engine will suck in a bit of the aerosol starting fluid and you'll hear the idle speed change from the mixture change. Just be careful about how much you spray, hot metal surfaces, etc. You should have a fire extinguisher on hand in your garage anyways