First, replace that o2. It's not related to your problem, but no one wants
to buy more gas or pay for a new catalytic converter after dumping unburnt
fuel into it.
Does your scanner read data, or just pull codes? If the former, look for the
barometric pressure from the mass air flow sensor. A common problem with
Ford MAF's is the hot wire getting dirty, and sending high-altitude readings
to the computer. Clean the screen and hot wire first, replace if that
doesn't work. The IAC code could have resulted from bogged-down idle, from
which the poor little motor couldn't recover.

J

Vito wrote:
>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