Deceleration Mode
WARNING: This page is about a different car, the 2004 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
When the driver releases the accelerator pedal, air flow into the engine is reduced. The PCM reads 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 catalytic converters.