No, you can use both; that way the IAC and ignition will work together to find the right idle speed.
Its useful in an instance where the IAC might not be able to support an idle RPM by itself (heavy load like AC running, electric fans running, headlights, defroster, everything loading the engine), you are giving the ECU permission to add timing to help raise (or lower) the RPM.

 

Thank you for the clarification; I presume the target RPM values need to be identical in Idle Control General and Idle Ignition Advance to avoid conflict.

 

Adjusting the General window should automatically adjust the values in the spark advance window.

 

Related question,

My IAC valve seem to be on its way out, but I'm planning on picking up a VEMS in the near future. Is it possible to delete the IAC completely and use ignition based idle control only? Can this account for temperature changes in the winter?

Thanks.

 

Yes you can do that too.

 

I have another question pertaining to cold start, coolant temperature 20C.

The motor will start but immediately dies. When I crack open throttle, the motor will start and continue to run but not very well. The motor will die when let off the throttle. During the initial warm up, the AFR is 11.5 -12. The motor will continue to run without throttle input after 60 seconds.

The symptoms suggest the motor requires more after start air. My understanding is this can be done with Idle Air Valve Reference Position. My question is what does RefDC % represent, the duty cycle of the IAC? Increasing the RefDC % value will open or close the IAC?

The default (no power) position of the IAC vale is approximately 15% open. Using the IAC Lock tool; I increase the duty cycle until the valve moved. I found valve did not move from 0 – 67 % duty cycle. The valve is closed at 75 % duty cycle and wide open at 82 % duty cycle. I verified the test results on two IAC units.

My questions are, is the relation between the duty cycle and the valve position correct? If the answer is yes, them should the PWM Idle Control, Min PWM Duty Allowed bet set to something greater than zero, such as 75%?