Originally posted by DennyW
Or, if you have a portable vac pump, hook that to the main vac going inside the vehicle, and listen. Then, hook it to the brake booster, and listen. This way you won't need the engine running, and you can eliminate the inside sources as the cause. Oh, and if you stick your head under the dash, make sure your not driving,
Good disclaimer, Denny, or he might end up like the guy with the Winnebago.