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What is a realistic rpmdot/CL idle rpm error?

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  • What is a realistic rpmdot/CL idle rpm error?

    Just finishing up some stuff on my tune. I'm seeing occasional rpmdots of 30 rpm and sometimes as much as 50, but I don't know what an acceptable level is. I don't want to spend any more time on it if that's normal. It's mostly less than 10 rpm.

  • #2
    Interesting question - I actually never thought about RPMdot values at idle. FWIW I'm seeing similar values as you are for both the RPMdot and CL idle RPM error.


    • #3
      iirc, rpmdot is used for locking out (disabling) closed loop idle on throttle changes - as long as it's not straying beyond the lockout, you should be good. idle error % isn't too much concern either - you don't want MS reacting to every error, otherwise it'd be too aggressive and start surging.

      Basically - if you're idling well, don't worry about it.


      • #4
        Yeah, exactly. RPMdot max, TPS threshold and MAP min are conditions that have to be met before CL Idle will "engage". Beyond that, I spent my time tuning the PID settings to kill oscillations. Once you get a stable idle, RPMdot is academic.


        • #5
          I really meant what counts as “stable.” If my tiny oscillations are normal, I know my tune is good enough.


          • #6
            Are your tiny oscillations following the IAC valve?

            A good tune for idle isn't really about flatness of RPM though, it's about the ability to not stall or surge in different environments (hot, cold, load changes, fans kick on, etc).
            Last edited by iscariot; 01-14-2018, 10:01 AM.


            • #7
              My closed loop is solid. I don’t think I was very clear in what I was asking. I just wanted to how solid the rpms should be at idle.


              • #8

                That is a screenshot showing my car idling for about a minute. The idle would hover at 850, occasionally rising as high as 900 and dropping as low as 750. Hope that helps. I can share some logs if you need.

                Edit: I uploaded a better screenshot. Use the one that lists RPM, MAP, CL Idle correction, and RPMDot.
                Attached Files
                Last edited by CAKELIE; 01-14-2018, 05:55 PM.


                • #9
                  Awesome. Thanks!