low idle warm 90 jeep 4.0

Hi Folks:
I have a '90 Cherokee Laredo injected 4.0. When it's warm, after
I've restarted it, it goes through this phase:

If I let it sit and idle, it will slowly go from say 1,000 RPM to 600
or so, and it will be fine. It I step on the gas at all, even if it's
just pulling away from the gas-station pump, it will drop to almost
stalling speed. Once in a while it does stall. Instead, if I let it
idle for about 2 minutes, this doesn't happen. I've changed the O2
sensor, a few of years ago. I've put about 30k miles on it since.
Could that be bad? The last time it STOPPED doing this was one time I
had the gas-tank down to change the pump, which I've done twice so far.
Maybe it's Jersey Gas. This might be something that clears up when I
disconnect-reconnect the battery. I'll have to try that again. Or,
maybe there's a chip upgrade?
Thanks!
Harry