Idle PID settings

[Ainis]

Hi,
anyone knows what "39 means 2,5%/1000RPM" means in the Idle control PID settings in the P description?

[gunni]

It means that there is a 2.5% duty cycle change for every 1000rpm of error there is between rpm and your idle target.
78 would mean that there is 5% change for every 1000rpm

[Ainis]

It means that there is a 2.5% duty cycle change for every 1000rpm of error there is between rpm and your idle target.
78 would mean that there is 5% change for every 1000rpm

Im still a bit lost with it. So I should use IAC lock and watch duty cycle at 1000rpm and then 2000rpm? Then I should find a difference between it and divide by 2,5 and multiply by 39? Then it would be my P value?

[fphil]

39 is just the code for the parameter of the proportional action P. Beware, for some reason !? (2.5% each 1000rpm) this action is nonlinear since the duty cycle added is proportional to the actual duty. This implies that the regulation even good when the engine is warm is instable (pumping) during warming. Manage to  use only the integral action (I term) - which is not itself much academic

[Ainis]

http://www.vems.hu/wiki/index.php?page=PIDControlTuning it talks about slope of the duty vs RPM, but RPM is 400 instead of 1000 and no percentage is mentioned 

[fphil]

I am unable to understand what is written (I have done control systems for many many years) besides this text dates back from 2007, things may have change from this time.
Engine warm get a stable idle 10-15% under the desired value without IAC, then tune I. If your RPM data values are not too noisy in order to fine tune you can then add P - to faster the tracking to the (moving!!) target,  and D (to avoid pumping)

[gunni]

It means that there is a 2.5% duty cycle change for every 1000rpm of error there is between rpm and your idle target.
78 would mean that there is 5% change for every 1000rpm

Im still a bit lost with it. So I should use IAC lock and watch duty cycle at 1000rpm and then 2000rpm? Then I should find a difference between it and divide by 2,5 and multiply by 39? Then it would be my P value?

No.

If your base is 50% Duty cycle and you have a 200rpm error, lets imagine no I or D, and your P value is 39, then

1000/200 = 5

2.5 / 5 = 0.5

Your added P is 0.5 and your total duty cycle is 50.5%

[Ainis]

Continuing this topic. Is it better to set ref idle dc to maintain idle target, or as manual says, +200-400rpm? Running DBW.

[gunni]

The ref DC should maintain idle target without any PID control, the PID control is there for the ECU to react to changes to the original circumstances like when you turn up the radio, put the ac on, lights on etc, all of those things will put more load on the engine.