Festiva L4-81 1.3L SOHC EFI (1989)
Fast Idle Cam: Description and Operation
When the choke is set during cold start up, fast idle cam position is determined by the choke thermostatic coil. The spring pressure exerted by the coil
does not act directly on the cam. Its motion is transferred through a choke lever and a fast idle cam link. When the choke plate closes, the lever rotates
and through the link moves the cam to the fast idle position.
Before the engine starts, the choke positions the cam so that the throttle lever stops against the high step. In this position, the throttle is opened wide
enough to allow atmospheric pressure to enter the carburetor venturi and draw the fuel required for starting. When the engine starts, intake manifold
vacuum is used to move the cam so that the throttle lever stops against the second step of the cam. Repositioning of the cam is necessary to reduce the
fast idle speed that would occur on the high step of the cam.
The intake manifold vacuum used to reposition the cam operates through a vacuum servo mounted on the carburetor choke pulloff. When vacuum is
applied to the servo, its diaphragm and link pull the cam to the lower fast idle speed position.
The vacuum signal to the Fast Idle Cam Pulloff diaphragm is controlled by a temperature sensitive valve located on the underside of the intake manifold.
The valve reacts to engine coolant temperature. When coolant temperature is below 50~C (122~F), the valve is closed, not allowing any intake manifold
vacuum to pass to the vacuum servo. When coolant temperature rises, indicating the choke is "coming off," the valve opens the vacuum passage.
