You can use the Idle control valve controller to pulse the valve to make it control the idle speed cleanly - but it will require a lot of experimentation.
In Extras->Idle Settings General
Set Control Type from ON/OFF to PWM/Stepper
Ensure that under Iac Hardware setup is of Type PWM, the channels should be correct as they are setup to drive the solenoid at the moment.
Then its down to experimenting. The values in the Idle Settings page should be straight forward.
Extras->Idle Settings Advance/PID give you:
Ignition based Idle control - this advances and retards the ignition to smooth the idle out, keep it disabled while you are trying to tune idle, as when you turn it on you will find that it has a large effect.
PID Idle Controller - this sets up the P I D controller, and its a black art to tune, I'd suggest that you google PID controllers in your native language to get an overview of what happens here.
Idle PID ref table, PWM - defines the 'position' that the IACV should be at for each temperature cell.
