Hyundai Repair: error code, mass air flow sensor, mass air flow

Question
I have a 2001 Hyundai Accent 1.5L with 65000 miles. P1123 manufacturer control fuel air metering code keeps coming up. I have replaced the mass air flow sensor, throttle positioning sensor and had a complete tune uo done at a professional garage. Any suggestions? They also recommended a new timing belt because Accents are known for breaking them around 60 - 70k. Is this true?

Answer
P1123 indicates the engine control module (ECM) perceives a rich condition.  I'd suggest primarily investigating two possibilities:

-- Stuck open purge valve.  This will cause fuel vapors to be sucked into the engine through the valve, creating an actual rich condition.

-- Upstream oxygen sensor erroneously reading rich.  If this is the case, I'd expect the downstream oxygen sensor to have normal or lean readings.  You'd need a scan tool to check this.