I had the k&n kit on both a Yj and a LJ with 4.0 motors. They seemed to calm the idle down a good bit plus , how do I put this...., free it up some ? It didn't feel as restricted as with the stock intake.
I also had a helix 1" throttle body spacer on the LJ and it "felt" as if it gave it a little more torque off the line. It also made much more noise for some reason.
But everyone has different results , that's why there is so much controversy over them. It also seems like it depends on the engine size as well.
2005 Jeep Grand Cherokee , 5.7 hemi,Blistein HD shocks and struts
, Eibach pro-kit , 20" SRT Reps, Nitto NT420s 275-55-20 tires, AFE stage 2 dry cold air kit Billet Technology catch can
, Imatation leather disco steering wheel cover
..... more to come