When the TP sensor’s signal indicates closed throttle position and the engine is idling, the ECM adjusts the idle speed control actuator so that the engine runs at the correct idling speed, regardless of coolant temperature, load and etc. When the additional load applied in the engine, the air flow through the idle speed control actuator is increased momentarily to raise the idling speed. The idle speed control actuator is the double coil type and has two coils. The two coils are driven by seperate driver stages in the ECM. Dependibg on the pulse duty factor, the equilibrium of the magnetic forves of the two coils will result in different angles of the motor. In parallel to the throttle valve, a bypass hose line is arrange, where the idle speed actuator is inserted in.
If the real engine speed is higher than the target engine speed at idle, the ECM judged as a fault and DTC is set.
Item
Detecting Condition
Possible Cause
DTC Strategy
? Real engine speed & target engine speed are monitored
? Poor connection
? Air leakage
? Hoses for crack/ connection
? Defective ISCA
? Open or short in ISCA circuit
? Defective TPS
? Purge control solenoid valve (PCSV)
? Defective Accelerator cable
? Defective ECM
Enable Conditions
? Idle speed control "ON"
? Engine coolant=75?(167?)
Threshold value
? Real engine speed > Target engine speed + 200rpm (time that above fulfilled =10sec)
Diagnostic Time
? Continuous
MIL ON condition
? 2 driving cycles
The left waveform is the voltage signals generated when ISCA operates at idle. This ISCA type is duty type and the time ratio opened determines duty amount.