Idle control

Algorithm

Fast path idle control is done through ignition. Slow path idle control is done through a base lookup map, and then adaptive closed loop control.
During cranking ISV DC is fixed from a map based on ECT.
Once the engine starts the idle setpoint is taken from the setpoint map and a base ISV duty is taken from the precontrol map, after which a closed loop controller modifies it.
There is no logging for the idle control in the fast logger. You can use VCDS to log it in normal diagnosis, or perhaps it will be added to the fast logger someday.

Maps

• Idle setpoint RPM - target idle RPM based on ECT.
• Idle ISV Linearization - target ISV DC based on RPM and ECT. Simply rev up the engine and then release the throttle, and see how slowly the idle drops. Keep in mind that the ISV can control airflow slowly - you want to have a stable base value, and then have adaptive control and ignition fast path to do the rest.
• Idle ISV Linearization, AC ON - same as above, but when the AC input signal is received by the ECU.
• ISV frequency during cranking - these two maps are added together and the duty cycle of the ISV during cranking is output from them. If you have more displacement or funny cams you might want to increase this somewhat. Same effect as slightly leaning on the throttle when starting the car (which you should never be doing if this map is tuned right).