Spark Idle (Idle Dyn)

I am playing with the tuning of a ecu off a UTV and this unit has A/C in it and has issues with idle stability when the A/C is turned on.

They changed the mapping from all zeros to what is shown in the graph below.

What I am failing to understand is if 0 represents the rpm the idle is set at w/o A/C on and everything to the left would be idle rpm error in the negative direction and to the right idle rpm in the positive direction.

So would it make sense to remove spark timing when the rpm drops to try and stabilize rpm once the A/C is turned on?

As you can see on the left side the gray line represents 0 and below that removes spark advance and above adds spark advance.

I am stumped why they would do that and hoping someone here can set me straight if I am wrong or verify the way I am thinking would be correct.

Idle speed error could be Target RPM - Current RPM, in which case you would add timing to provide more torque when the RPM is lower. That matches the table you've shown.

But if it is Current RPM - Target RPM, then it would be as you describe, and the table doesn't make much sense.

I think it's more likely that the Idle speed error is Target RPM - Current RPM given that table. Can you log or see Idle Speed Error with your software to confirm?

Hey David, Thanks for the reply!

Here is the idle taken from the spreadsheet where it shows Target Idle, Engine RPM, and RPM Error.

In the sheet it doesn't show a negative or positive value using a formula but easy to just look at and see if the error is either +/-.

Let me know if that makes sense to you using the previous graph as spark compensation for idle error, It makes sense to me that if the error is + then it would pull spark timing and if - then add spark timing and that would be using Target Idle as reference.

I added a marked up image and that is my thinking that doesn't mean I am right on the way I am looking at it.