Error Code P0172

Our 2001 PT Cruiser check engine light is on and the car is idling roughly
and has poor low-speed throttle response. The error code is P0172 that
states the oxygen sensor reports the air/fuel mixture is too rich and the
computer tries to add more air to compensate.

The gas mileage is pretty bad, ~15 mpg, at the last fill-up. The local
dealer wants to replace the fuel pump for $700. He said the fuel pressure
is too high, but when I checked the manual, it was within 2-3 psi of the
stated specification.

Does anyone have any suggestions? Would another oxygen sensor correct the
problem?

Thanks,

- Russ