Operation CHARM: Car repair manuals for everyone.

Deceleration Mode

Deceleration Mode
When deceleration occurs, the fuel remaining in the intake manifold can cause excessive emissions and backfiring. When the control module observes a fast reduction in throttle opening and a sharp decrease in manifold pressure, it causes the system to enter the deceleration mode by reducing the amount of fuel delivered to the engine. When deceleration is very fast, the control module cuts off fuel completely for short periods.