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Thread: Gen4 idle tuning guide

  1. #1
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    Gen4 idle tuning guide

    Hi guys, I have spent countless hours trying to nail down a good, concrete method for tuning gen4 vehicles. Today I finally came up with a consistent method to dial in base airflow that I haven't seen posted before, so I wanted to share it with the community. This guide is for airflow and the adaptives only, so I am going to assume fueling is already dialed in if you decide to try my methods.

    Before I dive into the steps, I want to briefly go over how the idle works on the gen4 pcm. There are 5 main areas that control idle: Airflow final minimum, base idle spark, spark over/under speed, proportional airflow, and integral airflow. These tables work closely together to attempt to keep your idle error to a minimum. Airflow final minimum is just your base air before any corrections. Base idle spark is self explanatory, as is over/under spark. Proportional airflow is an instant airflow correction based on real time rpm error. Integral is an offset airflow correction that gets applied to your airflow final minimum based on error over time. Proportional is to STFT as integral is to LTFT. It is your run of the mill PI controller, except it has different factors depending on how severe the RPM error is (the higher error, the more correction, and vice versa).

    The problem is, the adaptives are way over tuned from the factory, so as soon as you put an aftermarket cam in that oscillates significantly more than the factory cam, you end up with a very over reactive idle. You get spark going one direction, over correcting, then airflow correcting back the other direction since it is a much slower correction than spark. It is a vicious cycle as spark correction competes directly against airflow correction.

    The problem with just setting base airflow and calling it a day is you are tuning against two moving targets, the airflow correction and the spark correction. It's akin to trying to tune your maf table while the ve table is still enabled.

    What you really want to be do is turn off the adaptives completely, lock in your spark, and find your optimal base running airflow. Base running airflow is nothing more than base TPS %. So how do we do this?

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    **Step 1, find Airflow Final Minimum**

    Turn off all airflow adaptives, lock in spark, and set your target idle RPM

    The highlighted tables are the ones we need to change.

    1. Over and under speed delay needs to be maxed out.
    2. Proportional and integral enable rpm needs to be maxed out
    3. Proportional and integral airflow tables need to be zero'd out
    4. Airflow limits needs to be zero'd out.
    5. All follower tables should be zero'd out (on rpm tab and airflow tab)
    6. Set all idle RPM tables to your desired idle RPM. Use your judgement here. Obviously a big cam is gonna have to be pretty high. Start higher than you think as it is easier to tune down, than tune up.








    Lock in idle spark

    1. Set your entire high octane and low octane tables to desired spark value. I start high, with something like 24, and use the scanner to dial it in. Turning off the idle adaptives makes the normal spark tables get referenced for idle. For this reason, we don't need to touch the over/under spark tables.





    Set the airflow final minimum
    1. Set airflow final minimum. Like RPM, I start with a little higher than I think it is going to be so the idle isn't hunting too bad before stabilizing.
    2. Optionally, if you know your idle MAP already, set the surrounding baro cells to the same value. For instance, my car in park idles at 50 kpa, so I set the 50 kpa cell and the 53 kpa cell to the same value. We want to avoid as much TPS flutter as possible.
    3. Start by dialing in neutral/park. If you are auto, the steps will be identical, except you'll be using first gear.


    Last edited by BigMike42; 06-15-2016 at 08:41 AM.

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    **Step 1 continued**

    Find your best idle

    1. With the car fully warmed up and A/C off, start her up.
    2. Gently depress the throttle so the RPMS go up a bit, to say 1500 or so. This is going to knock you out of idle correction and bump you into the main spark tables. You have 409 seconds before adaptive idle comes back after every blip.
    3. Let the idle stabilize, you may have to have some finesse with the pedal to keep her running. If it's wanting to die on you right off the bat, increase idle airflow.
    4. Once the idle is stabilized, your spark should be locked to the value that was set and your TPS should also be locked. If you see any TPS fluttering, you may have missed an adaptive airflow setting. If your idle is wildly oscillating, you need to raise base airflow, idle rpm, or both and start over.
    5. Take note of the idle quality. What I do is log desired idle RPM and actual rpm, plot them on the chart with identical ranges (say 500 to 1200 rpm), and take note of where my actual RPM is in relation to desired RPM.
    6. By adjusting base airflow, base spark, and target RPM, find the best possible idle. Everyone's definition of this is different. My definition is minimal idle oscillation (minimal lope). I suggest shooting for this as well, because even if you want a lopier idle, that is easily achieved by adjusting the spark over/under correction later on.
    7. I also log RPM error (actual - desired) and shoot for +5 to +10. I'd rather it be slightly over the mark, than under it.


    Too low idle air looks like this (8.4g):



    Too high idle air looks like this(10.4g):



    Just right idle air looks like this(9.5g):




    Turn idle settings back on
    1. Set your idle RPM tables back, tapering down from factory to your newly found idle rpm.
    2. Base airflow I keep the same values at my target RPM and below and 1-2 cells above that rpm, then I just add some grams to the higher RPM values to keep RPMs from dropping too fast.
    3. Set over/under speed delay back to stock
    4. Set proportional airflow back to stock, optionally use the settings from a CTSV (they are pretty good from the factory). Integral still uses these values in the PI equation, that is why you need to populate them back.
    5. KEEP proportional rpm error maxed out, we do not want instant airflow corrections as they throw the idle off too quickly
    6. Set integral airflow limits back to stock, or optionally use the 2010 CTSV settings
    7. Set integral airflow back to stock or optionally use the 2010 CTSV settings.
    8. Set the integral RPM to around 12-15 rpm
    9. Set all follower tables back to stock (both on the rpm tab and airflow tab)
    10. Set high and low octane spark back to stock or whatever you had in there before, it will not get referenced for idle anymore.
    11. Set entire idle spark table to the spark you found. I just set the entire table block to the same value here to keep it simple.
    12. Spark over/under speed tables have to be heavily relaxed from stock. You should only need minimal spark correction. If auto and stock stall, in gear needs to have barely any correction or you will get bucking when your foot just comes off the brake. See image below of my tables.
    13. Set coast down spark to the same as idle spark, I will post more on how to adjust this table later, but for now this should be ok.




    My over/under speed tables


    My base airflow table



    After adaptives enabled

    Once you start the car back up, let the idle settle. Your spark should more or less be pretty constant to the value you set. Your TPS should also be at or very close to the value you found. If the TPS is oscillating a lot, your integral settings are too aggressive. Pay attention to the TPS you found during base idle airflow discovery and compare it to the TPS you are seeing after adaptives are on. They should be very close. If the TPS is WAY off, you have to massage your integral values around the 32 cells. Positive cells are for when the idle is below target rpm. Negative cells are for when the idle is above target rpm.

    What I found on my car was that I liked the idle to stay slightly above target before trimming down, and I also liked the TPS to come up quicker if the idle fell below target. So what I did was take the positive 32 cell and multiplied by 1.5. I took the -32 cell and multiplied by .5. What this does is when I come to a stop, the idle stays 20-30 over target for a split second and slowly drops down back to target rpm. Before making this change, it would drop too quick and overshoot.

    The goal is to have your idle look as good or better than it did when the adaptives were off. The actual RPM should travel along nicely on the desired RPM line in the chart's view. Log TPS and RPM error. TPS should average close to what your base airflow represented. RPM error should be slightly positive.
    Last edited by BigMike42; 06-16-2016 at 12:42 PM.

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    reserved for explaining how to slow down RPM descent during coast or blipping the throttle.
    Last edited by BigMike42; 06-06-2016 at 10:09 PM.

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    Smoothing out the 2-1 in automatic cars

    Cammed autos sometimes may have an issue going 2-1 coming to a stop. If torque management is engaging on the closed throttle downshift, what happens is your idle will drop way too fast, and then overcompensate back the other direction. Idk about you, but this pisses me off and is extremely annoying.

    The first thing you need to do is eliminate the timing pull. I can't speak for all ECMs, but removing limit torque management gets rid of the timing pull for my car and I still get to keep my rev matching. If that doesn't work, you need to turn off CT downshift, which will unfortunately get rid of rev matching. Try the limit tq management ect enable first to see if the timing pull goes away.



    Ok now that you have the timing pulled, engage a 2-1 stop. One of two things will happen:

    1. The car is either going to stop with minimal fluctuation
    2. The car is not going to dip down below idle, but the RPMS will annoyingly rise 500+ rpm from the lack of timing being pulled.


    If you're the first one, congratulations. Normally this will happen if you only had to run minimal timing and airflow for your cam. But if you have a cam with some overlap, you probably have pretty decent spark and airflow values, so you will get a spike.

    My "trick" to fix this, and it is a bit of a trick...almost a hack, but it works pretty well, is to use the coastdown spark table as my pseudo torque management downshift table.

    What I do is put around 8 degrees in the entire coastdown table. If your car has over/under speed for coast, make sure they are zero'd out completely. That's part 1 of the trick. This is going to guarantee that the car will only see 8 degrees of timing during any coasting downshifts. 8 degrees is about the highest you can go before the RPMs start to flare.



    The problem now is that the RPMs are going to drop faster because we have such little spark in the coast table. You can solve this by doing either of these methods or both:

    1. Base airflow table. Add some air to the cells above your idle. Go 1g at a time, log and retest.
    2. If that is not enough, subtract from the integral airflow table between the -96 and the -512 cells. Take away 10% at a time and retest.


    Once these are set properly, there should be no dip below idle RPM as you let off the throttle.

    Another problem with such little coastdown spark is low speed coasting is going to sound like your car is dying. What we need to do is bump the idle speed further out.

    Set the adaptive idle MPH to the same value as your 2-1 closed throttle shift MPH. In my case, it is 7.2 mph.



    Ok you may be thinking now, if we set the idle mph to the same mph as the 2-1 shift, we won't get the 8 degrees of timing.

    That is where the idle adaptive delay comes in. Increase the adaptive over/under delay to hold the idle spark out until the shift is complete. The bigger your idle spark/coast spark disparity, the larger the number will be. My example below is going from 8 to 22 degrees spark and while there is a slight RPM jump, it is vastly improved over before when it was just shifting at the full 22 degrees spark.



    Play with the idle MPH and idle adaptive delay until you like how the car is stopping. If you can get it to look like the below chart, it will feel pretty smooth.



    One more trick that can help the little under rpm blip....

    Give the rolling idle 10-15 mph of lead time. So if your target idle is 700 rpm, set 710 rpm to all the cells over 0mph. Some cars come like this already from the factory.
    Last edited by BigMike42; 06-09-2016 at 09:00 AM.

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    reserved 5

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    Interesting process you have there..... I like the concept. So while you're at it, how about adding some steps for start up - through the cycle where the ecm transitions to closed loop.
    When arguing with an idiot, make sure he isn't doing the same thing....

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    Quote Originally Posted by Michael_D View Post
    Interesting process you have there..... I like the concept. So while you're at it, how about adding some steps for start up - through the cycle where the ecm transitions to closed loop.
    Most of that type of stuff is by feel, but I can post what I change for the different scenarios.

    -If the idle is hanging on cold starts after the process above, I just turn the ECT airflow multi down in the colder cells 10% at a time until it's good. Unfortunately, takes full cool down every time
    -If the cold start up is fine, but warm restarts are dull..
    a) I modify cranking spark. My g8 settings have weird negative spark in some of the warm cells, I set these to 8-10 degrees all the way across in the hot cells.
    b) If that's not enough, I add 1g/s airflow to the hotter cells in startup airflow. I will add a max of 4, but usually some more spark and 1-2 grams is enough.
    c) If it still doesn't start well on warm starts, you can either add or take away fueling from the cranking fuel table. It will be trial and error.

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    One other thing I want to emphasize...

    You want to tune spark for idle quality, not necessarily map value. Why? Because as your spark goes down, your TPS is naturally going to go up causing your map value to also rise (and vice versa). But this doesn't necessarily mean your idle quality got worse just because the map got higher. Case in point, since my car is auto it idles the smoothest and drives the best at only around 12-13 degrees of spark. In a manual car, going a little higher on the spark could smooth it out a bit.
    Last edited by BigMike42; 06-08-2016 at 01:13 PM.

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    Added more detail to "After adaptives enabled" section.

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    Thanks for putting the time into this. It's much appreciated. I bookmarked it to come back to whenever I need to as a reference.

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    Quote Originally Posted by ridenrunwv View Post
    Thanks for putting the time into this. It's much appreciated. I bookmarked it to come back to whenever I need to as a reference.
    No problem, I am still ironing out how to fine tune the integral, so I will continue to update. Finding correct base airflow and base spark is very easy with this method though, so I hope some people try it out.

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    Some interesting stuff here. Curious how results are for others who try it.

    Nice contribution !!!
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    Quote Originally Posted by realcanuk View Post
    Some interesting stuff here. Curious how results are for others who try it.

    Nice contribution !!!
    Thanks

    Played with some integral settings today. Seems like the car likes a tight integral rpm (12 rpm) , but very relaxed integral airflow correction values. Barely any correction at 32 to 64 rpm, which is what you want. But the tight integral RPM ensures your throttle is going to stay in that tight range. The 2013 A6 vette has very good settings much like the CTSV. Later cars really don't need to do much with the integral, but earlier cars definitely do. The integral on my 2008 is super aggressive and causes wild fluctuations.

    Just for fun, I turned back on my proportional airflow and all hell went loose, so disabling this table or pushing it out much further is definitely helpful. In stock form, it probably never comes into play anyway except for on coast down. But of course when you get a cam, your idle oscillates much more, so it's coming into play in a fashion it was not designed for from the factory, so I recommend just deleting it.

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    Added 2-1 downshift trick for automatic cars @ post #5.

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    Good thread

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    Added tune for reference. The '13 vette integral settings work awesome. I did have to modify the coastdown a bit as it was a bit too aggressive below target rpm. I just set them to the same as the normal idle. Tested my method posted above again to find exact base airflow and it's silky smooth. Only hiccups I get are on hot restarts, but that is because of heatsoaked IAT. Nothing I can do there really, except maybe command 1.10 fueling.

    g8-idle-best.hpt
    Last edited by BigMike42; 06-09-2016 at 06:40 PM.

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    I'm going to try copying your idle settings and see what happens
    Post a log and tune if you want help

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    Alright, I just straight copied your settings to see what happened. Def. idles smoother than I think it ever has. When changing gears it will drop from say 2500 to 1500 RPM's slightly slower than it used to (but fast enough..) then from 1500 to idle it takes 3-4 seconds for it to slowly drop down, so that was the only issue I had. I wasn't logging this morning so not sure what is causing it, but I'm going to try to spend some time on it this weekend. I noticed timing was pretty low during the 1500-->idle RPM time so I'm guessing min air is too high, just a guess though.

    I might just switch it back to my old settings.. you can't really tell my car has a cam in it anymore it's so smooth, lol

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    Quote Originally Posted by schpenxel View Post
    Alright, I just straight copied your settings to see what happened. Def. idles smoother than I think it ever has. When changing gears it will drop from say 2500 to 1500 RPM's slightly slower than it used to (but fast enough..) then from 1500 to idle it takes 3-4 seconds for it to slowly drop down, so that was the only issue I had. I wasn't logging this morning so not sure what is causing it, but I'm going to try to spend some time on it this weekend. I noticed timing was pretty low during the 1500-->idle RPM time so I'm guessing min air is too high, just a guess though.

    I might just switch it back to my old settings.. you can't really tell my car has a cam in it anymore it's so smooth, lol
    Sweet! Yeah it's all personal preference, but since my G8 is my baby hauler I wanted it as smooth as possible, which sent me on this quest to find out how the hell all these tables interact with each other.

    If it's dropping too slow, remove base air from above 1000 rpms. If it's still dropping too slow, add to the coast down integral table in the -96 to -512 cells. Try doubling it first just as a sanity check. There is also the torque follower table that definitely comes into play, but I haven't figured out exactly how yet. I know negative numbers means subtract torque (less tps) and positive numbers add torque (more tps), but it doesn't seem as sensitive to change as the integral, so I haven't really touched it.

    My tune only has 8 degrees spark on coastdown to help make the 2-1 smoother, so I needed more TPS. That is also another way to get the RPMs to drop faster, just drop spark down on coast.
    Last edited by BigMike42; 06-10-2016 at 08:16 AM.