Remove the IACV, plug it in, have a friend turn ignition on/off and see if the plunger moves at all.
It is a Jeep 4.0 IACV that is a direct fit, I think a GM 4.3 works as well but dont know for sure.
It sounds like your IACV is stuck open and letting in to much air.
If you have not removed and cleaned it yet start there, also clean the port it mounts into.
I dont remember what type of screws hold the IACV on, make sure its that you remove and not the TPS, the TPS is the closest to the throttle mouth.
2nd owner of a '97 Disco with a ARB winch bumper, SD roof rack, Rover Racks ladder, Cooper S/T's and 220,000 miles on the clock and still a daily driver.