Idle Control Settings

Contents:

Idle Control Setup Procedure

This procedure will guide you to easily setup VEMS idle RPM control functions, we will show how to verify idle control valve hardware operation, setup open loop RPM control and in the final step enable closed loop RPM control

Before proceeding to tuning of the idle RPM with running engine we first we need to verify proper operation of the idle valve itself with stopped engine.

disconnect the idle valve from its housing or connected tubing to be able to see the internal position.
make sure the valve has power applied to it.
adjust PWM frequency to around 100Hz, set min duty to 0% and max duty to 100%
use test function in VemsTune, its available under VT->Tools->Iac lock, make sure you are getting a larger opening (more air) when you enter a higher number, if the control direction is reversed, invert the output channel.
take care some valves have a limp home position in the beginning before the actual larger opening comes into view, if so make note of the required duty cycle to get passed the limp-home section (on the iac duty cycle gauge) and enter this into the min duty (in iac hardware settings).
once the idle valve hardware verification is complete attach valve back in housing and re-connect tubing.

Before starting the next part of the procedure it is imperative to verify that any functions that might prohibit easy setup of idle RPM are disabled.

In VT->Base Setup->Rev Limit/Overrun/Safety disable:

overrun fuelcut, enter fuel-cut RPM = 3000 rpm above highest idle target and fuel-resume RPM = 2800 rpm above highest idle target.
lowmap fuelcut, enter a very low value, like 0 kpa.

In VT->Starting/Idle->Idle Control PID:

disable idle PID feeback control by setting with P=I=D=0

The following adjustments require running engine, start the engine and let it idle (if required manually apply some throttle):

make sure the mixture in the idle area is properly tuned if its is far off target make sure to adjust the VE table first until around target, it might be needed to adjust warmup enrichment at the same time.
now adjust the iac reference curve (in VT->Starting/Idle->Idle Reference Curve) as the engine warms up. Aim for RPM 200 RPM above the requested target for that coolant temperature.
repeat the cycle as many times as needed to get the full curve filled, let engine cool in between adjustments.
adjust the cranking postions (in VT->Starting/Idle->Idle Reference Cranking) and fill these with same values as the cold and warm positions with same temperature from Reference curve (slight up or down offset might help starting).
if properly tuned the engine should now start up and idle stabily around 200 RPM above target in all engine coolant temperatures.
reenable low map fuelcut and overrun fuelcut as needed, recommended settings: low map fuelcut 20kpa below map value at idle RPM, overrun fuelcut 700 RPM above highest idle target, fuelresume 500 RPM above highest idle target
you can think about reenabling PID control, but only if engine runs and starts normally now. Suggested starting values for PID can safely be used from defaultfirmwareconfigs/config_1.2.23.vemcfg included in your VT install dir, make sure to import only these settings using the IMPORT button in the idle control PID settings dialog.
tuning PID control in general is not VEMS specific, experiment with different loads on engine (enable alternator load by turning on lights, wiper, window defogger) and retune PID values to get stable (transient) response.