Engine Hunt at Idel

[aussieboxy]

I gave a 2000 2.7 that hunts at idle. What I mean by that is that the idle speed will drop to about 400rpm and the jump up to about 1500 rpm. It does this constantly. It's not quite as bad one you put the aircon on but it's still annoying.

Any idea's on how I can fix this problem.

Thanks guys.