At first was hard to start, but will now start but idle poorly (almost
stalling, then smoothing out repeatedly). Also lack of power on
acceleration.

I poured my monthly can of B-12 Chemtool into the gas tank a couple of days
ago - I've never had problems before doing this in over 230K miles.

Pulled the IAC and cleaned it...no change.

Pulled all plugs and cleaned them...no change.

Pulled codes P1504 (Idle Air Circuit) and P0153 (O2 Sensor circuit slow
response; Bank 2 Sensor 1)

Any ideas of where to look next?

Vito