I've been exploring the forums attempting to find an answer to a problem I have been having but this problem seems to have a unique location. I have a squeel coming from the throttle body even after going through 3 different sensors and pcv valves/ vaccuum lines. I've cleaned the throttle body out and attempted to spray every inch of the intake and throttle body to find leaks in the gaskets. The squeeze usually only happens when it is under 50° and gets worse as the engine warms up with it only happening at and around idle, sometimes it does make the sounds up to half throttle but not often. I pull a vacuum line off the intake manifold and the sound will almost dissappear although the vacuum being pulled seems to be excessive as it is also causing all of the pcv valves to slightly whistle. Anything helps or even a direction to figure it out as I'm scratching my head on this one. 2000 4.0 with 206,000 miles

 

My 01 used to squeal only at idle and had it narrowed down to the butterfly shaft on the throttle body. I had a spare so I changed it out. when you can duplicate the noise paint a good bit of vaseline on both outsides of the shaft to see if it stops or reduces