sense the throttle is cable operated on this model,,i don't see how this could happen..i agree with your son,that it isn't the o2 sensor ..for the engine to rev like this ,it would need to get air,the only thing that i can think of that may cause this is the iac[idle air control]valve
IDLE AIR CONTROL (IAC) VALVE REPLACEMENT REMOVAL PROCEDURE
INSTALLATION PROCEDURE NOTE: The IAC valve may be damaged if installed with the cone (pintle) extended more than 28 mm (1 - 1/8 in) . Measure the distance that the valve is extended before installing a new valve. The distance from the idle air control valve motor housing to the end of the idle air control valve pintle should be less than 28 mm (1 - 1/8 in) . Manually compress the pintle until the extension is less than 28 mm (1 - 118 in) .
sorry.i had a little computer trouble here
i wouldn't think it is the tps..this wouldn't raise the engines rpm