1990 Jeep Cherokee engine Idle Problem

I have a 1990 Jeep Cherokee Larado, 4 speed automatic, with a I6 4.0 engine.
It starts fine, runs great at speed. But when I come to a stop with the engine on it has a very unstedy idle. It feels like its missing, but the lurches it makes are come pleatly random.
It can do it 20 times in arrow befor retuning to a nomal idle or once. My Question to you is, Do you know whats causing this fault, and is it fixable?