The throttle switch is not included on all models. Look where the accelerator cable connects. If you have the throttle switch, you will see a small switch mounted to the throttle body with a roller on it. The switch is activated when the gas pedal is pushed all the way down. A cam on the throttle lever closes the switch contacts, signaling to the ECU that full-throttle mixture enrichment is needed.
This switch does nothing more than tell the ECU to enrich the fuel/air mixture (more fuel) when the engine is at full throttle.
The switch can be tested. Measure the resistance between the two switch terminals. With the throttle closed it should be infinite ohms. Then open the throttle all the way, you will see the cam close the switch and hear the click, at which point the resistance reading should drop to near zero ohms. If the switch doesn't quite make it, it can be adjusted where it mounts for proper functioning.