Sluggish backfiring cherokee

1999 cherokee sport inline 6 cyl. (4.0L) approx 63000 kilometers fuel inj.
Problem is A few hundred yards after startup when engine cold,the jeep
get jurky and will backfire unless I let up on the throddle or stomp it to the floor and then it will go. It starts fine and only acts up for the first
few miles then it is fine.I brought it to the dealership and they could not
find the problem ,there are no engine codes .I have done A tune up
(plugs ,wires, rotor and cap) no difference,I suspect the MAT air
sensor A ohm reading is about 20000 ohms cold to below 3000 ohms
operating temperature, this seams to be in line with the Haynes book I
have although it only gives the reading at operating temperature.
I am not sure what to do next , any help?

definitely sounds as if the engine mixture is too rich upon start up.
Try testing the throttle position sensor, when the engine is cold.

My '96 Jeep Cherokee is giving me exactly the same problem - did the advice on the throttle position sensor prove corect?

No it did not help next I am considering the MAT
sensor

Keep in mind, if it was the MAT or the TPS there would be a code, those are computer related. Check you timing. There might be a issue there, or in your distributor.

Changing the MAT sensor seams to have taken care
of the problem,so far it is running fine.

No MAT sensor did not do the trick seamed ok for A
few days but the problem is back