Mixture Control Solenoid - Slow Cut: Description and Operation

Slow Fuel-cut System:

When the throttle is closed (deceleration) and the engine speed is high, manifold vacuum increases significantly. This can draw large amounts of fuel through the slow (or idle) circuit, causing a rich condition that can damage the catalytic converter. The slow fuel-cut solenoid valve closes off the primary slow fuel circuit during deceleration at high engine speeds, preventing the over-rich condition.

When the solenoid is OFF (de-energized) the primary slow fuel circuit is blocked. When the ignition is turned "ON", battery power is applied to the solenoid. The ECU completes the circuit to ground when the engine is started. This energizes the solenoid and opens the primary slow fuel circuit. When the idle switch is closed and the engine speed is greater than the set point (approx. 2,500 rpm), the ECU opens the ground circuit. The solenoid is de-energized and the primary slow fuel circuit is closed off, until the engine speed drops below the set point.