Sluggish backfiring cherokee

1999 Cherokee starts fine I go 200 -300 yards and then it is sluggish
backfires and just seems jerky on off for about 2 miles then it is ok.
I have done A full tune up (plugs,wires,cap,rotor) no change ,there is
only 65000 kilometers (approx 40,000 miles) I took it to the dealer no
help the technician agreed about the symptoms but because there were
no diagnostic codes present did not now what to say but bring it back and leave it with me for A day, (at $80/hr) .I suspect the cold air sensor
but because it runs ok at start up I am not sure . No other problems with the jeep . Any ideas or direction would be helpful.

I once had a plymouth mini van that had small
"air pump" valves that screwed right into the cylinders
from under the valve cover.
They were small enuff that the "valve heads" would just burn off
or get full of carbon and hold open.

I would be driving down the highway and it would lose more and more power,
I could pull over, let it idle for 1 minute, take off and all be ok,
for about 5 miles or so, then repeat.

I replaced the exhaust system, fuel cap, and forgotten now, but many things until i found these lil valves one day when i was yanking the head off just to give all a good going over...


lol




just a thought!!

see if you have small air jet valves *in* your cylinder

: )