The term "opened throttle" is often associated with increased speed, power, and acceleration. However, some antonyms for this phrase might be "reduced throttle," "closed throttle," or "minimal throttle." These expressions would denote a decrease in speed or power, often used when decelerating or coming to a complete stop. Other antonyms might include "idling," "coasting," or "braking," indicating a slowdown or the absence of power being applied.
The choice of antonym depends on the context in which the phrase "opened throttle" is used. If discussing the acceleration of a vehicle, "closed throttle" might be the most appropriate antonym. However, if referring to the behavior of an engine while waiting at a stoplight, "idling" or "minimal throttle" could be more suitable.