1997 jeep grand cherokee 4x4

When I first got this(1997 Jeep Grand cherokee. 4.0,automatic) it idled like crap(between 1,000-4,000RPMS and constantly changing) So I replaced the IAC motor. Great it idles pretty good and consistant. Still though daily when at a stop sign and left to idle of a couple minutes, it will go from good to very poor and almost stall out. Like it is running out of gas and has no power.

Currently has check engine light on for to much voltage to upper bank O2 sensor.

just change the sensor its not a hard job to do and it cost 30$40$depend on the quality you buy
after diconnect the negative pole of your batterie for 5 minutes to erase the check engine light

If the stalling continues after this repair, then you may have a bad Crankshaft Position Sensor. It's common on that year after 80-90k miles.