Vacuum leak

[TexasRN]

Hey all.

2013 Expedition Limited 135,000 miles. No codes present. I'm hearing a vacuum leak under the passenger side of the dash. I'm also getting some bucking under acceleration. It goes away once I'm cruising. I originally thought it would have to do with blendors, but my reading says that those are all electronic my the 3rd gens. It is definitely inside. I don't hear anything under the hood.

Any ideas how to track this down? I'm hoping that fixing the leak will correct the bucking.

 

[eddytheexpy]

Any chance it could be the vacuum tube that goes up kind of behind the throttle body (I forget exactly what it connects to). That guy is right up against the firewall. AFAIK, that vacuum hose has the highest likelihood of making a sound that could be appear to come from the inside.

As for "inside" noises coming from the passenger side, that's where your heater core lives. Maybe something wacky is going on with your coolant system? This is a total guess based off nearly zero specific knowledge but if your thermostat is acting up, the coolant might be getting too hot in the engine and boiling then the vapors wind up in the coolant system. These vapors could cause noises in your heater core and an over heating engine can definitely act up. Then once you're cruising and the thermostat finally "wakes" up, it starts doing its job.

Again, this is an absolute wild ass guess. So anyone reading this, feel free to call me stupid but please tell why I'm stupid as I'd like to broaden my understanding of things.