1989 jeep cherokee 4.0 cuts without warning or when you let off gas pedal

I know this is two years after you asked, but I've had this same model for fifteen years. The crank sensor needs replaced about every two years, and I've found that having the ignition system cleaned helps. That crank sensor also seems to lead to fuel pump issues so if replacing it doesn't help, look at the fuel pump. The part runs around $15, labor is about one hour ($45 around here). Have your transfer case cleaned up when it's done, although most mechanics would do this anyway since the sensor lives behind it. Fuel pumps are more, of course- the part starts at $100 through some online sources, labor seems to be two hours.

Check the crank position sensor and the throttle position sensor