When you turn the AC on it open's the throttle to raise the RPM's . I think it also slows the throttle from closing to fast which would cause a jerking motion.

That boot is nothing more than a dust cover. I wouldnt worry about it to much. <img src="/forums/images/graemlins/kewl.gif" alt="" />

98 Montero with cold weather package
96 Toyota Land Cruiser, fully locked Mall Machine :-)