2004 lariat S.crew 4x4--this morning, a sound in the rt front wheel area directed me straight to the mechanic, after a search and spinning the rt frnt wheel freely, sounds as if it is trying to engage into 4wd (the switch is in 2wd also). My first go round w/ this. Mechanic tells me it is the vaccum actuator sensor if i am correct. Removed the vacuum line and there was some slight suction too, on both lt/rt, is that normal when in 2wd? Question is, is this common, do both lt and rt get replaced or individually or one unit only. Is it a easy fix to do or let mechanic do it...is it costly too? thanks for any feedback...

 

I had vibration and turns to be that a vacuum leak the mechanic put a new right line and problem solve, check lines to see if they are broke good luck.