Considering that the IAT sensor is on the +5 volt supply, the max voltage should be 5 volts. So 12 volts indicates a short to battery positive. If this were my car, I would be looking to see where the wiring harness could have been damaged during the repair.
IMO based upon the DTC code and the recent repair, replacing the IAC is a waste of $$.
P0113 - Intake Air Temperature (IAT) Circuit High Input
Indicates the sensor signal is greater than Self-Test maximum. The IAT sensor maximum is 4.6 volts or -50°C (-58°F).
Open circuit in harness
Sensor signal short to power
Improper harness connection
IAT V PID reading greater than 4.6 volts with key ON and engine OFF or during any engine operating mode indicates a hard fault.
2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.