My youngest daughter has an '01 Dodge Durango, 4 wheel drive, automatic,and 4.7 engine. With the air off it idles smooth and accelerates fine. When you turn the air on the idle jumps up to about 1200 rpm comes back down to about 800 or so and fluctuates from then on. At speed it does the same thing, but it doesn't always do it. It's got a little over 108 thousand on the clock. I was thinking a partially clogged fuel filter, but the filter is in the tank. Anybody have any ideas?