Here's more info then you want, i'm sure...

Code 1-2-1

If the signal from the MAF sensor is lower than 0.2 V or greater than 2.2 V at idling speed, or is considered unsatisfactory according to RPM and throttle angle, this is interpreted by the control module as a fault and DTC 1–2–1 is set.


Substitute value
-The control module uses engine speed and throttle angle to determine the load.
-The IAC valve's idle air trim is inhibited.
-Long term fuel trim inhibited.
-Only initial charge pressure is permitted.
-The EVAP diagnosis is inhibited.


Possible source

Signal too high:
-Signal lead short circuited to voltage supply.
-Break in lead to signal or power ground.
-Defective MAF sensor.
-Contact resistance in connections.


Signal too low:
-Break in signal or voltage lead.
-Signal lead short circuited to ground.
-Damaged or loose fresh–air hose, upper charge air cooler pipe or lower charge air cooler pipe.
-Defective MAF sensor.
-Contact resistance in connections.


Fault symptom[s]
-Uneven idling and/or jerky operation.
-Poorer performance from initial charge pressure limit.


Code 4-1-4

The ECM calculates charge pressure by using the signal from the MAF sensor. When the ECM considers that the MAF sensor is correct and the load signal exceeds a preset level, DTC 4–1–4 is set.


Substitute value
The system only permits initial charge pressure.


Possible source

-Defective MAF sensor.
-Contact resistance in connectors.
-Break in the lead to the charge pressure reduction from AW 50–42.
-Clogged hoses between turbocharger (TC) and TC control valve, and TC control valve and pressure servo respectively.
-Defective TC control valve.
-Defective pressure servo to the wastegate valve.
-Seized wastegate valve.


Fault symptom[s]
-When charge pressure reaches the max. limit, fuel injection is stopped. As a result, the engine becomes very jerky.
-Poorer performance from initial charge pressure limit.


If I'm reading this right, it seems that your computer believes the MAF is right and the load is wrong. So most likely would be a bad MAF, though other things can cause it. It would be more labor on your part to check everything else but easier on your pocket book not to start with the MAF...