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I went ahead and made a video to cover the basics on PCM operation, tables and their relations, and some physics. Should be very helpful for folks just getting into or want to learn how to tune. Sorry it's kind of long, but it was a lot to cover. Could have been worse lol.
I really appreciate the feedback guys. I'll keep putting these together, and sharing every trick and understanding of tuning I know. I'll work on some scanner stuff next time maybe, or some other fringe areas that don't get covered much like EOIT (injector timing). That and some of the calculation formulas for cylair (airmass/dynamic air) and how the PCM gets the values. I have some cool formulas that can help with tuning or checking VE on newer cars that can really break it down, however I left these out this time because I wanted to keep it simple for this one lol.
Math seems to scare some folks lol. Another reason is I want to be as accurate as possible, and show it the best way I can, and considering the amount and complexity of the formulas, it might be difficult to make it clear and understandable without even more research. Basically I need to find the end of the internet again to make sure I have it right before I share it with you guys, because the model years are different in the displayed values on the VE. On our older PCM's it goes by percentage VE basically, at least what it appears to be that is, which is still something I need to figure out to make a useful formula on it. Newer ones display 3 or 4 digits, which is the raw number not percentage, which is actually much easier to get from the calculations, because they come out to 3 or 4 digits with the numbers plugged it.
If anyone knows the formula for the older GMVE conversion to percentage, then I'm all ears lol. I've probably already found it, but I need to dig a bit further to further my own understanding of it. I just haven't been able to plug a formula in yet that converts to raw VE in my older PCM. Did the other ones for a 14 Camaro and get the numbers no problem.
Or I could just cover how it works on the newer VVE tables, because it's pretty easy on those, and also shows what values do what, which helps in understanding the various sensors and their functions, to say the least.
Thanks again guys, you are motivating me now lol, so I'll keep them coming.
Curious about WARM/HOT start IAC readings & settings.
When and HOW, should they be addressed?
I know in your IAC video you mention the one log being taken when engine was warm, I believe?
I have a weird, and very intermittent idle surge when engine is HOT. I never addressed Base Running Airflow, as I've never seen, or found, the infamous "russk" config, to try and use.
ChopperDoc - awesome stuff. I subscribed so keep 'em coming lol. Everything is spot on with my research, understanding, and practice over the last 2 years. You were able to clear things up for me for idle tuning. I knew how to do everything but didn't know/understand the order of adjusting things so it took me 2 weeks to get my idle dialed in through trial and error. Definitely an 'aha!' moment and will save time in the future.
I would suggest a quick 'these are the tables the car is using when it's idling/Accel/decel/etc' would be nice. I found that there were a lot of how to's for specific things, but not a take-a-step-back once you know how to do those things. I obviously learned best figuring it out on my own, but think it would help the step above a beginner with troubleshooting by understanding when the car jumps from idle tables to main tables, etc.
rel3rd - I'll see if I have the russk config and send it to you if I do.
Curious about WARM/HOT start IAC readings & settings.
When and HOW, should they be addressed?
I know in your IAC video you mention the one log being taken when engine was warm, I believe?
I have a weird, and very intermittent idle surge when engine is HOT. I never addressed Base Running Airflow, as I've never seen, or found, the infamous "russk" config, to try and use.
You can build the russ k RAF table pretty easy. Plot "idle desired airflow" on the ECT table axis from your RAF. Then don't hit the throttle while it warms up and put the numbers into the table (make sure you are using the same units). They are direct copy over, perhaps I could do a video on it this weekend.
However I think that it might be another issue to why you are surging. If you IAC is closing all the way and the PCM can't control the idle air, it can easily cause that. Watch your IAC counts and see if they go down to 0 before it starts surging. Pretty common issue. If so, simply close the blade 1/4 turn at a time until counts are between 20-80 while hot. You want enough for the car to warm up while cold, but not too little that the IAC closes off when it's hot. I usually shoot for about 40 counts for normal idle.
As for HOT and warm, you can tune the IAT anytime really. How much of the data you will see will depend on how cold the engine is when you start. The IAC will be nearly full open on a cold day, and close slowly as the engine warms up. Engine needs to let more air in and add more fuel to warm up because fuel doesn't like to burn in cold, dense air. There's a happy medium with that, when the fuel becomes a vapor easier, and it doesn't do that too well when temps are freezing lol. We used to call this "cold blooded" back in the day for cars that hated cold mornings. My diesel truck is another story entirely there, but same thing, takes a lot to warm it up and damn near half a battery to start it when it's below freezing.
I have mine set to pretty much "good enough" for a non-daily driver. It starts and warms up fine when cold, but only if it's above about 35* out. I tried it under that and decided that it's not worth going out to start it in those temperatures with that thing anyway, and it's better to use the remote start from the safety of my house for the caddy instead lol.
Thanks for the tips.
I've done the IAC logs and reflashes 5 times now and am much closer than when I started.
I attached latest log below
As for the surge, there seems to be no rhyme or reason for it. One stoplight, it'll idle great for 5 minutes straight, then 4 stops later may fluctuate for no known reason.
Also attached a log of a basic drive from shop to home last week.
I seem to always only have limited time to "fix" this thing, so any guidance is welcomed.
Thanks for the tips.
I've done the IAC logs and reflashes 5 times now and am much closer than when I started.
I attached latest log below
As for the surge, there seems to be no rhyme or reason for it. One stoplight, it'll idle great for 5 minutes straight, then 4 stops later may fluctuate for no known reason.
Also attached a log of a basic drive from shop to home last week.
I seem to always only have limited time to "fix" this thing, so any guidance is welcomed.
Your IAC motor is definitely hitting zero, does many times through the log, which would explain your surging, potentially. What I can't quite figure out is also why it keeps jumping up to 330 suddenly and randomly. I looked at the throttle cracker table to see if it was speed related, but it occurs at different speeds and the RPM's also do not line up with a cell on that table. Pretty weird it does that. Seems steady state the the IAC just opens with a mind of it's own lol.
Have you altered the effective area table? The adjustments shouldn't be drastic. I'm trying to figure it out still because at idle your counts are like 130. Could also just be a bad IAC motor too. Definitely a possibiilty given it's behavior.
Could also be the "rolling idle" settings too. I saw 2 spots it jumped from low 40's to 340 at exactly 34 MPH. Still very odd unless you have that table set to infinity or something, right at that spot. It also does it at 54 or so, which is not a cell on that table so leads me to think it might be a mechanical issue. You could try a reset on it by unplugging the sensor, key on for 5 seconds, key off, hook it up and clear the code. It's the same as a TPS reset.
I just noticed that your "desired" IAC position remains unchanged when it goes haywire. In other words, the PCM isn't telling it to do that. It just does what it wants... If it hasn't been changed in a while, the motors can go bad. Yours is being pretty insubordinate according to the log at least lol.
I just noticed that your "desired" IAC position remains unchanged when it goes haywire. In other words, the PCM isn't telling it to do that. It just does what it wants... If it hasn't been changed in a while, the motors can go bad. Yours is being pretty insubordinate according to the log at least lol.
Yeah, that is weird. It was transferred over from the stocker, to the new TB late last Fall.
I have even tried re-flashing known "trouble-free" tunes just to see if it was some sort of fluke.
I attached my current tune.
Car was originally (when I got it) a turbo car.
3 bar SD RTT OS. I took the turbo off a year ago, and re-added a MAF meter and just have my over 105 kPa numbers artificially high so as not to confuse me.
You may be onto something with the IAC itself. The car actually idled smoother, and more consistent without any tuning after the cam swap I did over the winter.
FWIW, I installed a new Delphi IAC and nothing seemed to change, but it is 80 degrees and sunny, so I took it for a drive anyway.
When I got home, I tried loosening the throttle blade screw to see if I could get idle IAC counts to move one way or another...
I then noticed the throttle cable would not let it return to the throttle body stop...
Added a little play to the cable and started over and was able to get idle iac counts to 50-60 in park and then drive it back to work to park for the night.
I did log the drive back, so will upload it tomorrow morning and see what it looks like. It seemed to idle fine, so hoping it was a fluke
Here are some values you can try because I noticed your Base RAF table is practically stock. Your values are so low it could cause these issues. You can use either of these numbers. The first picture is "desired cs ECT."
And this is "Dynamic vs ECT."
Either way your RAF table is way too low. You can also try reducing your throttle cracker values as well, because they seem very high in the rolling idle region, nearly 4 times the stock values.
Edit: Note that I am using grams/second (g/s) here, so make sure you are using the correct units in the tune when plugging these in. You can use either one really, I actually usually plug in the dynamic values so it's closer to the VE calculations.
Last edited by ChopperDoc; 04-23-2019 at 11:48 PM.
I still need to research as to how the PCM calculates "desired" exactly, as I do not know the exact formula, (yet that is, more experiments to do in excel lol) but the Russ K idle config table is the first pic, and the second is the same thing except dynamic plotted on the same values. Dynamic seems to work, and in my experience with a 3rd gen PCM, the RAF table doesn't seem to do as much as you want it to when trying to control what the IAC is doing. I will say that your effective area is fairly close actually, so don't play with that until you have the RAF table fixed. Your log is actually a good example as to how much those numbers don't seem to affect the actual "desired" since the table values are around 6 g/s, literally half of what is showing in reality. This doesn't mean it doesn't have an effect on the "effective area" or other tables though, just that the physical "desired" seems to be a number of it's own, and I am yet to discover the actual calculation and what it effects exactly. I can say it's obviously not helping you though lol.
04-19-2019, 04:50 PM
Introduction to HP Tuners for Beginners 
