XFI IAC "P" and "D" gain values

[CS99]

What do the values do? I have my "P" gain set to 30 and "D" gain set to 4. I want the idle to come down a little slower after startup. Do I raise the "D" gain value?

 

[TurboBuRick]

From Fast website:

11.5.1 IAC “P” Gain
The IAC "P" gain value can be set from 0 to 255. Raising this value will cause the IAC motor to open or close further in an attempt to correct the idle speed. The default value of 32 for the P gain is generally close to correct for most applications.
11.5.2 IAC “D” Gain
The IAC "D" gain value can also be set from 0 to 255. Raising this value will cause the IAC motor to open or close faster in an attempt to correct the idle speed. The default value of 4 for the D gain is generally close to correct for most applications.
NOTE - An excellent way to better understand these settings is to liken them to a sensitivity control on a cruise control circuit. If the circuit was set for maximum sensitivity (gain values both set to 255) the accelerator pedal would go to the floor as soon as you dropped below the target speed, and the pedal would drop to an idle as soon as you were going too fast. If the circuit was set for minimum sensitivity (gain values set to 0) the accelerator pedal would hardly move if you were going too fast or too slow, and you would almost never be traveling at the desired speed. This same concept applies to how your IAC motor will regulate idle speed.

 

[kidglok]

I want the idle to come down a little slower after startup. Do I raise the "D" gain value?

If you want the idle to come down slower after staring once the car is already warm, then you need to raise the starting iac pos vs coolant temp.

If your talking about cold start routine then you can scale the idle speed vs coolant temp to drop gradually down to what you want your idle speed to be.


raising the D gain will make the iac close faster and thus making the rpms drop at a faster rate, you want to do the opposite although i wouldnt reccomend it because it might make the car bog down when coming to a stop at a traffic light etc.