Tunerstudio Closed Loop Idle Auto Tune
Oct 09, 2018 This is my approach on idle tuning. I go over every step - what I'm looking at, looking for, and tips and tricks on what to do in a bunch of different situations. Idle tuning can be frustrating. We provide do-it-yourself and fully assembled MegaSquirt fuel injection systems, MS3Pro engine management systems, & accessories to help you tune your car!
I've setup closed-loop idle control for my 94 Miata similar to how Braineack and others have set theirs up[1]. I am using MS2Extra 3.2.1 with a DIYPNP. PWM Warmup mode works well and I can set idle with the valve at a fixed duty cycle at the end of the warmup map. The MS reliably enters closed-loop idle when the throttle is released; however, I am ending up with oscillations. I watched the PWM Idle Duty and noticed that the valve would close and open correctly for entering and leaving closed-loop idle. Once the algorithm kicks in and starts altering the duty cycle, I get large swings in idle RMPs. What I am seeing is that the valve doesn't respond for 5% intervals in PWM idle duty and then responds all at once. Idle jumps 200+ RPMs suddenly. The algorithm then repeats the slow change in PWM idle duty in the opposite direction until it crosses the 5% delta again and the RMPs jump 200+ RPMs in the other direction.I have attached a data log of using the idle valve test mode to adjust the PWM idle duty across the thresholds where the jumps occur and then back again. The log was captured with the valve frequency at 13*30.5. This is the frequency that the base map uses for the 94 Miata. This lines up with the '@156Hz the valve works in 2% steps' comment in TunerStudio right? ~400Hz works in 5% steps? I had much better luck tuning the algorithm with lower valve frequency, but the valve sounds like a prop plane at those frequencies.
I've tried making the algorithm more or less aggressive, but it seems that with a change of 100-200 RPMs across a 1% PMW Duty change that only occurs every 5% of duty cycle, the algorithm simply cannot find a happy position for the valve.