Idle Speed Control (ISC) is required to provide a stable idle speed as engine operating conditions change and extra loads are applied or removed. Without idle speed control, an engine will idle too slowly when cold or too fast when hot, often the cold idle speed will be so low that the engine stalls. Likewise, extra loads (such as air conditioning compressors switching on) will decrease the idle speed and may cause the idle to become unstable.
The ISC system regulates the engine idle speed by adjusting the amount of air which is by-passed around the throttle or by holding the throttle slightly open in the case that an ethrottle is used. Idle speed control can be achieved using a solenoid valve (two or three wire), a stepper motor actuated valve (four terminal or six terminal) or Electronic Throttle Control.
A description of each mode and it's requirements is provided in the Idle Actuator page.
Idle speed can be controlled using Open Loop or Closed Loop and Idle Ignition Control is also available for advanced users as additional control to the open or closed loop setup.
·Open Loop control simply sets the position of the ISC controller to a base position specified in the Idle Base Position Table.
·Closed Loop control compares the actual engine idle speed with the desired engine speed set in the Idle Target RPM Table and automatically adjusts to correct the difference between the two.
·Idle Ignition control provides settings to retard and advance the ignition during idle to help smooth the engine speed changes.
Open Loop idle control is sufficient for most applications and is easy to setup, Closed Loop idle control will produce a more stable and repeatable idle but is more complex and time consuming to setup. In both Open Loop and Closed Loop we can compensate engine loads using various corrections that are applied and removed when loads are applied to or removed from the engine. Closed Loop control also has Idle Up settings that can increase and decrease the target rpm as loads are applied to and removed from the engine.
More in depth information on the 3 modes is provided in the following pages.
Runtime Parameters
·Idle Status: all possible idle status are:
"Active" - it is on closed loop controlling
"OFF" - Idle control not setup or turned off
"OFF: RPM = 0" - Engine not running.
"RPM Target" - The idle speed has reached its current Target RPM (Closed Loop only).
"Open Loop Mode" - Idle Speed is operating in open loop mode.
"Crank % DC" - This indicates that the idle solenoid/stepper or E-Throttle is in its crank position.
"Hold - Throttle Open" - The throttle is open past the AP/TP Lockout position. Idle control is not active.
"Hold - RPM Lockout" - Closed loop control is disabled as RPM is greater than the RPM Lockout value.
"Hold - Speed" - Vehicle speed is greater than Speed Lockout. Idle control is not active.
"Dashpot Hold Time" - Idle Speed is now in Dashpot hold time stage
"Dashpot Decay Time" - Idle Speed is now in Dashpot decay time stage
·Idle Target:
Current Idle Speed Target.
·Idle Position:
Current Idle Speed Position which can be % Duty, Steps or % of E-Throttle Position.
·Idle Target Error:
Current target error which is the difference between the current Idle Target and engine speed.
·Idle Ign Angle
Current Ignition Angle in Idle