I have a 97 F150 4.6l, and this morning I noticed a noise that sounds like air sucking in. You hear it mostly at idle, the truck is idling where it typically does, but occasionally it will "bog" down a bit for a couple seconds, but then keeps running normally. Anyways the noise seems to be coming from the lower drivers side. Under the dash/steering column, and around the front drivers wheel well. Could it be a vacuum leak? The truck does have lean codes. I'm not sure if this is relevant but if I'm at a stop and I release the brake to accelerate the noise will stop for a split second once the pedal is released....any help is certainly appreciated.

 

Get under the dash and check for a vacuum leak at/around the input rod on the brake booster. Just follow the brake pedal linkage up to it.