I have a 2000 f150 xlt 5.4. I have a problem I can't trace. When I accelerate I hear nothing but when I lift my foot off the gas after execration I hear "whoosh" sound. I assume its a vacuum line but as I have to be driving to hear it loudly I can't trace it. Does anyone have a vacuum diagram for the 2000 f150 or know what I might check to remedy the problem? I've been spending days checking vacuum lines for a problem with no success.

 

Air filter ?

 

Its definitely not the air filter. It sounds like its sucking harder when I take my foot off the gas rather than when I accelerate. Under load the "whoosh" sound goes away.

 

Somethings connected incorrectly. When did it start happening? Need more info - try not to leave anything out.