Deceleration Mode

When the driver releases the accelerator pedal, air flow into the engine is reduced. The PCM looks at the corresponding changes in throttle position, manifold air pressure and mass air flow. The PCM shuts OFF fuel completely if the deceleration is very rapid, or for long periods (such as long closed throttle coast-down). The fuel shuts OFF in order to protect the warm-up three-way catalytic converters.