Throttle housing - ’K’ series

Throttle housing - ’K’ series

The throttle housing is located between the inlet manifold and air intake hose and is sealed to the manifold by an ’O’ ring. The throttle housing incorporates a throttle disc which is connected to the throttle pedal via the throttle lever and a cable.

There are two breather pipes connected to the throttle housing; one either side of the throttle disc. When the engine is running with the throttle disc open, both pipes are subject to manifold depression and draw crankcase fumes into the manifold. When the throttle disc is closed, only the pipe on the inlet manifold side of the disc is subject to manifold depression. This pipe incorporates a restrictor to prevent engine oil being drawn into the engine by the substantially greater manifold depression.

Mounted on the throttle housing are the throttle position sensor and idle air control valve.

Throttle housing - ’T’ series

The throttle housing is attached to the inlet manifold via a flexible mounting plate. The throttle housing incorporates a throttle disc which is connected to the throttle pedal via the throttle lever and a cable.

There are two breather pipes connected to the throttle housing; one either side of the throttle disc. When the engine is running with the throttle disc open, both pipes are subject to manifold depression and draw crankcase fumes into the manifold. When the throttle disc is closed, only the pipe on the inlet manifold side of the disc is subject to manifold depression. This pipe incorporates a restrictor to prevent engine oil being drawn into the engine by the substantially greater manifold depression.

Mounted on the throttle housing are the throttle position sensor and stepper motor.

Throttle position sensor

The throttle position sensor is a potentiometer attached to the throttle housing and is directly coupled to the throttle disc. It is non adjustable, closed throttle is detected by the throttle position sensor which initiates idle speed control via the idle air control valve.

The ECM supplies the throttle position sensor with a 5 volt supply and an earth path. The throttle position sensor returns a signal proportional to throttle disc position.

Throttle disc movement causes voltage across the potentiometer to vary. The control module calculates the rate of change of the voltage signal in positive (acceleration) or negative (deceleration) directions. From this the ECM can determine the required engine speed, rate of acceleration or rate of deceleration and apply acceleration enrichment, deceleration fuel metering or over-run fuel cut-off.

Idle air control valve - ’K’ series

The idle air control valve is mounted on the inlet manifold and controlled by the ECM. The idle air control valve opens a pintle valve situated in an air passage in the throttle housing, allowing air to bypass the throttle disc and flow straight into the inlet manifold.

By changing the amount the idle air control valve is open the ECM can control engine idle speed and cold start air flow requirements by adjusting the flow of air in the passage.

During cold starting the ECM indexes the idle air control valve open slightly to provide a level of fast idle, dependent on engine coolant temperature. As the engine warms, fast idle is gradually decreased until normal operating temperature is reached.