This is what the CD that came with my scanner says about code P1123

OBDII P1123 Fuel Trim Additive, System Too Rich

PRIMARY COMPONENT:

Air/Fuel Control System

SECONDARY SENSOR(S):

Mass Air Flow (MAF) Sensor
Throttle Position (TP) Sensor
Intake Air Temperature (IAT) Sensor
Engine Coolant Temperature (ECT) Sensor
Oxygen Sensors

FAILURE CONDITIONS

If the air/fuel mixture at idle is too rich for more than 30 seconds during two back-to-back trips, this code will be set and the Malfunction Indicator Light (MIL) will be turned on.

Details:


The code will be triggered if the following conditions are met:

Long term fuel trim value (additive) is less than -0.75 ms (-15% to -20%) for 30 seconds or more
Engine speed is less than 880 RPM )
Mass air flow rate is less than 6.1 g/s
Engine coolant temperature is greater than 158?F (70?C)
Engine in closed loop operation
No canister purge occurring