RomRaider

Good day,

While tuning a very large cammed rotated 2016 STI, I stumbled into a question I've always had but never bothered to ask. My normal process for tuning these cars is adjust idle stability, initial idle airflow and the associated counter until I get a nice return to idle. The one problem I've never been able to crack with these cars is coasting in neutral you will get that occasional slow oscillation (it'll settle at target idle, then after a second it'll blip up 200 rpms, then repeat).

So on to my question--why is there no ignition timing control while coasting in neutral? If you log it, you'll see instead of the varying ignition timing you only get a flat line (whatever value you have set for idle ignition timing). So the ECU is forced to try and use the throttle to control short term idle RPM errors. My understanding is that throttle adjustment is a "rough" adjustment to get close and ignition controls the rest.

I've taken a look in IDA and frankly I can't make heads or tails of the strategy. I suppose I'm beyond my skill level in this scenario.

Any and all help is appreciated.
Matt

There are 6 tables used for idle error ignition timing compensation depending on current conditions. They’re just not usually defined in most OS definitions


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Correct. They are all 3d tables with similar setups like the idle stability table. I believe off the top of my head they are in-error, out of error and and another set. My point is I don't think these are in use when "coasting" above the speed threshold.

They should be active as there is a target idle rpm speed even on coasting conditions, therefore it should be correcting ignition timing to keep that target idle speed.

I can define these compensation tables for you to do some testing, I’d probably need to pull out the rolling idle targets as well


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Hey there,

I believe I have them all already--I generally define these for any car I tune. Are these the ones you are talking about?

Also, you can see by the screenshot what I'm referring to in regards to idle timing. In the picture, the flatlined green line is coasting at about 15 to 20mph in neutral. I have personally seen this on every car that I've tuned. Tomorrow i'm going to get a log of my untouched Legacy Spec.B to see what it looks like during the same conditions, but I really do assume it'll look the same.

edit: I've also considered that rolling IN and OUT of gear idle RPM tables might cause something like this, but after seeing that "RPM" subtracted by "idle engine speed error" equals my target idle of 1000RPMs I'm inclined to think it's not relevant.

Yes, those are the ones I was referring to. I do also see a correlation between TPS and the rpm swings. I've found good results in more adjustment to throttle blade position than idle ignition timing.

But I do see what you mean as ignition timing flatlines at 10* even though it should be compensating based upon these tables

I can usually manage to slow or minimize the oscillation one way or another, I just figured it would probably be helpful to know why ignition timing is doing this--i know it would help drastically.

I appreciate you taking time to respond. Hopefully someone comes along and clues me in on why this is happening.