900 Turbo Convertible L4-1985cc 2.0L DOHC Turbo EFI (1994)
When the accelerator pedal is not activated and the throttle plate is closed, the engine only receives air via the idle air control valve.
The ECM controls the degree of opening in the valve to keep idling speed constant. This means for example that the valve opens slightly more when the
AC compressor is switched on or if DRIVE has been selected, in order to compensate the idling speed, which would otherwise fall.
The idle air control valve, which is single-coil, is supplied from the main relay. The valve is controlled from pin 49 on the ECM with a 500 Hz PWM.
The valve opens more the longer the ECM keeps pin 49 grounded.
The ECM is programmed to keep the engine idling speed at 900 ± 50 rpm. Rapid changes in idling speed cannot be compensated for with a change in air
flow. Ignition control in idling is instead designed so that engine speed is kept constant.
If there is an open circuit to the idle air control valve, the opening in the valve is set by a spring so that the idling speed is at least 1000 rpm when the
engine is warmed up.