Find another mechanic. There a big difference between the IAC (Idle air controller) and the VSS (Vehicle speed sensor)
CODE 42 - Vehicle Speed Sensor - No "SPD" signal to ECU for 8 seconds when engine speed is between 2,500 RPM and 4,500 rpm (7M-GE) or 4,000 rpm (7M-GTE) and coolant temp is below 80 deg. C (176 deg. F) and neutral start switch is off. Trouble areas - Vehicle Speed Sensor Circuit, Vehicle Speed Sensor, ECU.
The speed sensor is located in the instrument cluster, and a part of the speedometer. You may need to find a new one.
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