Except Pickup, 4Runner, MR2 & RWD Corolla
The cold start system provides additional air and fuel during cold engine starts. The cold start system consists of the following: Cold start injector which delivers additional fuel, and a start injector time switch which controls operation of the cold start injector. Some models use an Idle Speed Control (ISC) valve, while others also use an Auxiliary Air Valve (AAV) to provide additional air during cold engine starts and warm-up.
The start injector time switch limits cold start injection to 1-12 seconds under extreme cold engine starts in relation to engine temperature. When engine temperature rises above a specified point, bi-metallic contact breaks ground circuit of cold start injector and cold start enrichment is by-passed.
The auxiliary air valve consists of an electrically heated bi-metallic strip, movable disc, and air by-pass channel. The heater coil on the bi-metallic strip is energized by the fuel pump relay. Control of the valve is based upon engine temperature; the air by-pass channel is open when engine is cold and gradually closes as temperature rises. At predetermined temperatures, air by-pass channel is blocked and additional airflow stops. See Fig 1.
The ISC valve performs the same function as the auxiliary air valve. Mounted on the throttle body, the ISC is a solenoid-actuated valve which provides additional air during cold engine operation. It also maintains idle speed during air conditioner operation. The ISC is controlled directly by the ECU.