Deceleration

When the engine is warm (at operating temperature) this is a Closed Loop mode. However, if the MAP sensor input is below the minimum programmed level, the system will enter Open Loop. The system will return to closed loop when the MAP sensor input rises above the minimum level. During deceleration, the following inputs are received by the engine controller:

- Coolant temperature

- Manifold absolute pressure

- Idle contact switch

- Engine speed

- Throttle position

- Exhaust gas oxygen content

- Park/neutral switch (neutral safety switch) (automatic transmission)

- A/C control positions

A closed throttle input, along with an abrupt decrease in manifold pressure, indicates to controller that vehicle is in a hard deceleration. The engine controller may reduce injector firing to once per engine revolution. This is done to lean the air-fuel mixture as sensed through the O2 sensor during hard deceleration.

The engine controller grounds the EGR and evaporative purge solenoids. This will stop EGR and canister purge functions. The engine controller may cycle air switching solenoid for short periods of time. This is done in response to the MAP sensor sending a high vacuum signal.