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Thread: How does everyone stabilize Idle Torque and/or Timing at Idle?

  1. #1
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    How does everyone stabilize Idle Torque and/or Timing at Idle?

    I have been through over 100 logs trying to get VVE and MAF correlated to what my wideband tells me, although I doubt my wideband sometimes. I thought the issue was I just didn't have VVE good enough and after messing with VVE and MAF this long its starting to make me think otherwise. No other idle settings seems to change a thing (torque reserve, PI control gains, VTT at idle region, etc.).

    Once the immediate torque control source goes to idle the timing starts jumping up and down almost going negative and then going back to almost 30 degrees, which causes really annoying bucking at idle and its especially annoying at rolling idle with the foot on the brake.

    You can see it here right when I put my foot on the gas the the immediate engine torque command source switches to axel from idle timing stabilizes:
    good.jpg

    To me all the other torque PIDs look normal. Zero pedal engine torque, immediate engine torque commanded, and delivered engine torque all say around the same value, my scanner shows I am sampling them all at the fastest rate although it looks to me like some of them aren't actually sampling that fast, so I may be aliasing some of the data since timing and rpm are jumping around faster than some of my torque PIDs seem to be updating. I am also running open loop since I have my wideband in place of my bank 2 O2 sensor.

    I still am trying to make sense of the confusing mess of torque PIDs, but it appears to me that the torque PID's agree, but its almost like the torque command is what's fluctuating and making the timing fly around trying to match it, I'm getting almost a 100 rpm swing at idle. I know I should bump my idle up but the issue does not completely go away until about 1000rpm idle.

    On a sidenote I just noticed my VVE table at the powerband region 5000-6000rpms is barely over or equal to the stock VVE table and I've adjusted it from wideband feedback, the lower rpms are 20-30% less, this just dosent make sense to me, but I had to take a lot out at low rpms and idle regions from stock though.

    20-03-13 15-21-36.hpl

    Fifty Tune Modified ECM_TCM_FICM.hpt

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    So I wanted to bring this back up. I think maybe this negative timing at idle has caused my cats to start failing, or it could just be from the overlap and extra unburnt fuel.

    I have tried all kinds of combinations of adjustments with the proportional and integral gain (which I am not entirely convinced it is a gain and also given it has units assigned to it (ft-lbs), I am thinking it could be a error value difference). I have tried all kinds of different settings for the external load and limit offset as well, which I don't believe should be adjusted from stock since the HP Tuners description says this table "models the engine load" which makes sense as it is based on oil temp which should make a big difference in how much torque is needed to turn the engine over.

    After messing with all the stuff trying to make sense of it and experimenting, I have basically concluded not much of anything besides if you deviate them too far from stock it will kill the engine. No matter what combination of values I try nothing will make the timing go higher, so the ECM is always trying to reduce delivered torque. The predicted control however will respond consistently no matter the gain values, so as the immediate control command pulls the timing back (sometimes to -20 degrees), the predicted will respond and open the throttle blade (sometimes to 20% or so).

    I am not a big fan of having to change the virtual torque tables that much from stock. Since I believe GM tuned in particular the airmass table to be accurate. So if I haven't fundamentally altered the combustion chamber design or significantly reduced friction losses then the porting and cam I have done will then just pull more airflow and then the PCM will reference higher airflow torque values in the tables. That being said I understand sometimes we can't do everything exactly right given we don't have full access and control and we will have to do work around. For example, I think it is necessary that I update the MAP based torque table since the engine could theoretically make more torque with the same MAP value from stock. Also it may be necessary to slightly bump the VT tables globally since I have increased compression. Is that logical thinking?

    So it appears that the trend is when I decrease VT in the idle range, I get extremely low idle timing until it eventually dies.

    When I increase VT I get extreme instablity in idle timing where it bounces from very high to very low values, so somewhere there is maybe some kind of discontinuity in the table references causing oscillation at idle.

    As always I really appreciate the help everyone puts in to help other with tuning as this stuff can become so frustrating. I really hope there is someone out there who has figured out GEN V torque based tuning with cams. I don't expect a stock like idle with a large cam, but it seems like I should at least be able to get timing under control.

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    So I realize the importance when you are tuning these GEN V controllers that VVE must be dead on since everything is referenced from the VVE airflow model. However, I have spent hours and hours logging correcting and reflashing to try to get VVE better.

    That being said I have tried a few other things. I rescaled the y-axis on the leading edge angle table for the high pressure fuel pump in effect to model the "32% increase" fuel lobe I have from my cam swap. I was really thinking this might be my issue but so far doesn't seem to have made any difference in anything, I didn't really have any large fluctuations in commanded versus desired high fuel pressure anyway. I also figured, especially since so much timing is being pulled and effecting combustion and combustion stability, that I would cut fuel pressure at idle. This did end up increasing pulse width a couple ms, but unfortunately didn't seem to do anything either.

    Its stressed so much and for good reason that VVE has to be dead on or you will be going around in circles, so I am pretty confident this has got to be my problem. The thing is I have spent months and months and log after log, logging histograms of wideband error and fuel trims in every which way I can think of and feeding that back into VVE and trying to correct. I just am going in circles as well, the error is not converging, I have tried many ways of filtering as well. I think the negative timing along with the high overlap in the cam bring in exhaust charge to dilute the intake is causing false feedback with the wideband.

    This wouldn't be so much of a problem if I could manually use the bi directional controls to force spark and throttle to where I need it to be but none of this is working since I have heard if your air models are off the commands won't work. However, I have found sort of a alternate method, I use the bi directional controls to lock the highest gear I can and force the TCC solenoid on. Then I go drive up and back up a hill so I can basically hold the engine at idle speed (500-600 rpms) but the torque source is axle not idle since I am moving the car at around 10mph. I feel like if I keep doing this though I am going to ruin crank bearings or the TCC clutch or something but hopefully not. I have done this countless amounts of time, but even with this my error is not converging, I wouldn't say its diverging either.

    I also have noticed it is having the same low timing problems at very very light throttle as well. I can watch it in the scanner and see that "axle" is my commanded torque source and see timing at 0-10 degrees and accelerator foot pedal position at around .5-4% I will be creeping along slowly up high at about 1 or 2 percent throttle and all the sudden timing will go to its normal 30 degrees of timing then all of the sudden drop back to 0 or 10 and you can feel the car stumble back and forth. Its really bad when you creep along with the TC locked in high gear and I go to lighter throttle where it starts doing the low timing stuff and it rattles the entire drivetrain and pinion gears back and forth and feels like the car is about to come apart.

    I just don't get it, how is everyone else doing it? I have heard that under +/-5% is the target, I just don't see how anyone is getting there given the instability of O2 feedback, inability to control timing, and error in back solving VVE coefficients.

    For some reason I can't get my log file to upload so here is a link to download:
    https://1drv.ms/u/s!AkCUE89IhD0Ng-B1...Z8eKA?e=IOtUdN
    Last edited by cmitchell17; 04-14-2020 at 11:22 PM.

  4. #4
    When you change the cam you change the air model which changes the torque output. Especially at idle. Torque is greatly reduced at idle with a larger cam. The vtt needs to be changed to reflect this. It takes a lot of time getting this right as it's more of trial and error. Start by unchecking the link selections box and make changes to each table individually. I'll start with reducing the torque by 20% in the rpm, airmass, and map in the idle areas of the -10 and 0 degree tables. Then 15% in the 10 degree, 10% in the 20 degree and 5% in the 30 degree. Larger cams I'll reduce 30% in the lower timing tables and gradient up from there. You also need to smooth the tables out from the idle cells up in rpm, airmass, and map so you don't just have a big chunk of torque removed from the idle areas and stock the rest of the table. Changes also need to be made all at once before you hit the calculate button. And once you calculate that's it. If you need to make further changes you have to go back to stock and start over. Otherwise you start to get too far out in the rest of the tables. If you're cam is not locked you have to make the same changes to the different cam angle tables as well. It's extremely time consuming, but I can get a large cam to hold the timing as smooth as a stock cam. This is the only way I have found to add significant amounts of timing at idle as well as smooth the idle timing fluctuations.

    I believe we are missing tables for idle control. My 17' 1LE idled at 0-2 degrees when it was stock. The first 17' manual Camaro SS I tuned started completely stock before we did bolt ons. That car idled at 10-12 degrees of timing stock. When I compared the two stock files the only difference was the external load table. I copied the SS table to my 1LE tune. Still 0-2 degrees at idle. Both calibrations were identical. Vtt, vve, maf curve all the timing tables, everything was identical, yet the SS idled with 10 degrees more timing.

    So for now completely restructuring the torque model is the only way I have been successful at adding timing at idle with large cams.

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    Quote Originally Posted by cmitchell17 View Post
    That being said I have tried a few other things. I rescaled the y-axis on the leading edge angle table for the high pressure fuel pump in effect to model the "32% increase" fuel lobe I have from my cam swap. I was really thinking this might be my issue but so far doesn't seem to have made any difference in anything, I didn't really have any large fluctuations in commanded versus desired high fuel pressure anyway. I also figured, especially since so much timing is being pulled and effecting combustion and combustion stability, that I would cut fuel pressure at idle. This did end up increasing pulse width a couple ms, but unfortunately didn't seem to do anything either.
    I thought that the thing to do for bigger fuel lobes was to multiply the entire 'Fuel Pump Flow Temp Corr' table by your new fuel lobe %.

    I hope someone will chime in on this one as I'm curious if I've been doing it wrong.
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    Quote Originally Posted by g26er View Post
    I thought that the thing to do for bigger fuel lobes was to multiply the entire 'Fuel Pump Flow Temp Corr' table by your new fuel lobe %.

    I hope someone will chime in on this one as I'm curious if I've been doing it wrong.
    scale the y axis is correct
    multiply table values is incorrect

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    I edited this axis by multiplying the entire axis by the increased fuel lobe percentage:
    Capture.JPG

    So I am assuming the pump doesn't know anything but now the controls have to know that a stroke now displaces 32% more volume than it did stock, what I don't get is how this y-axis even exists it seems like it should just be one constant value, and that value is the displacement volume of the pump, which the aftermarket cam lobe increases by so much percentage.

    So I learned this from Greg Banish's GEN V videos, which I really was not too impressed with, however I trust that he would know a lot more than what most people claim to know. There is a lot of information missing from his videos and he basically gives one example. He kind of insinuates, which I know its important to have a correct VVE airflow model, that VVE is the answer to all your problems and that's the only thing you need to do. For example of important left out info, he completely leaves out an explanation of all the torque PID's and how they relate the the tables we have available in HP Tuners.
    Last edited by cmitchell17; 04-15-2020 at 07:35 PM.

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    Quote Originally Posted by 32vape View Post
    When you change the cam you change the air model which changes the torque output. Especially at idle. Torque is greatly reduced at idle with a larger cam. The vtt needs to be changed to reflect this. It takes a lot of time getting this right as it's more of trial and error. Start by unchecking the link selections box and make changes to each table individually. I'll start with reducing the torque by 20% in the rpm, airmass, and map in the idle areas of the -10 and 0 degree tables. Then 15% in the 10 degree, 10% in the 20 degree and 5% in the 30 degree. Larger cams I'll reduce 30% in the lower timing tables and gradient up from there. You also need to smooth the tables out from the idle cells up in rpm, airmass, and map so you don't just have a big chunk of torque removed from the idle areas and stock the rest of the table. Changes also need to be made all at once before you hit the calculate button. And once you calculate that's it. If you need to make further changes you have to go back to stock and start over. Otherwise you start to get too far out in the rest of the tables. If you're cam is not locked you have to make the same changes to the different cam angle tables as well. It's extremely time consuming, but I can get a large cam to hold the timing as smooth as a stock cam. This is the only way I have found to add significant amounts of timing at idle as well as smooth the idle timing fluctuations.

    I believe we are missing tables for idle control. My 17' 1LE idled at 0-2 degrees when it was stock. The first 17' manual Camaro SS I tuned started completely stock before we did bolt ons. That car idled at 10-12 degrees of timing stock. When I compared the two stock files the only difference was the external load table. I copied the SS table to my 1LE tune. Still 0-2 degrees at idle. Both calibrations were identical. Vtt, vve, maf curve all the timing tables, everything was identical, yet the SS idled with 10 degrees more timing.

    So for now completely restructuring the torque model is the only way I have been successful at adding timing at idle with large cams.
    Thank you for the help. I believe at this point trying to get my VVE more accurate with wideband feedback, given that the ECM is pulling so much timing and therefore effecting combustion and skewing the accuracy of the wideband (I am suspecting I don't know if that's factual but it seems plausible), is going to be a waste of time. For now at least I am going to have to try your instructions and change the VTT.

    With all that being said I watched Greg Banish's GEN V videos, which I was not impressed with at all especially for the money they cost. However, he states in the video that you shouldn't be editing the VTT tables independently and that you should leave on the "link selections". I forgot what he was really getting at there but I need to go back and watch the videos again to try to pickup more info I didn't get the first time.

    Another interesting point he makes is that the way HP Tuners labels each table as spark=x, spark=x+5, spark=x+10 and so on depending on what you set the spark increments to is actually incorrect by HP Tuners. What I believe he was saying that basically each different spark scenario table is just another table based on how far away you are from the MBT table (which is a table you can adjust in HP Tuners in the ECM which HP Tuners says in their descriptions that adjusting that table is NOT recommended, even though it seems like Banish was recommending it if you have the appropriate mods). So instead of saying spark=0, spark=5, spark=10, I guess it would be like torque when timing is retarded from MBT by x amount of degrees. I would take it that you could go look up whatever is in your MBT table and say its 20 degrees, then you go to the table where HP Tuners says "spark=20" and that would be your torque at MBT. Although I could be wrong?

    Anyway I really appreciate your help 32vape, i'm going to go try it now if I can find some motivation.

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    Does anyone know of a good number to be within to make the airflow model correct on VVE? I've always heard +/-5%, but I am wondering if its good enough? I have doubts about the accuracy of a wideband in trying to get there especially given that we are measuring non-steady state, suboptimal timing conditions.

    Instead of using the built in HP Tuners EQ ratio error percentage, I am just using commanded/actual and directly multiplying that number (by half) to the VVE table for correction purposes. This method is recommended by Banish, although it seems like its going to do the exact same thing. I really question my practices especially since nothing will converge. Honestly it seems like I would have better luck blindly adjusting the VVE table up and down at idle speeds until things started looking better.

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    IMO, it shouldn't be +/- 5% it should be 5% so that is really +/- 2.5% but I like everything negative so I like it between .95 and 1.0 lambda in open loop tuning.

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    Quote Originally Posted by Higgs Boson View Post
    IMO, it shouldn't be +/- 5% it should be 5% so that is really +/- 2.5% but I like everything negative so I like it between .95 and 1.0 lambda in open loop tuning.
    Thank you Higgs, I agree, even a 2.5% increase at some rpms could cause a very significant airmass and corresponding torque change.

    So looking at it a little closer I feel like my VVE correction factors are definitely diverging. I've still been taking histogram logs and trying to correct the VVE table better when I started to notice more of a increase in torque reduction during part throttle shifts, I thought it was from my virtual torque table adjustments I was making by taking away torque at the lower rpms and idle range, but lookin closer I figured out it was cutting power becuase its getting so lean and the timing reduction at the shift is making it basically almost cut out and loose a lot of torque.

    Anyway there is something going on. I have the AEM wideband that has the integrated CAN broadcaster and there is a few PID (unit ID's) that I am getting whenever I select to log it and when I try to use it as an input to a math parameter. This is the actual PID I am logging for it and I know this has got to be correct as I can see its picking up its unknown "virtual module":
    Attachment 98462 https://photos.app.goo.gl/oELjGuax59FicSKh8

    But somehow things in HP Tuners get changed around when you go try to pull PIDs to use in math parameters and other things. I was initially using this PID for the error calculation in the math parameter:
    https://photos.app.goo.gl/grdtzsTDTTKXZbda6

    But I am not so sure this is the right one so I changed it to this one:
    https://photos.app.goo.gl/1qGiC5XTSrFAFXkV6


    However whenever I try it both ways it gives me what seems like the same error number that is correct and plausible. So I just don't get it, does anyone else see what else I could be missing or doing wrong? I think I am still having the same problem when I use the generic built-in HP Tuners errors, no matter how many times I log the histogram and reflash nothing just seems to converge?

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    Just a question are you still running your wideband sensor behind the cat in bank1 position 2

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    No the wideband is at bank 2 position 1 at the header collector merge.

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    So I really did'nt give this much though, but I believe what Banish uses in his video is wrong. He says he makes a feedback math to chart in the histogram that is Actual/Desired, which since I am running lean ( I can feel it and my wideband (in lambda) is reading higher than 1). If I take the direct value of actual/desired, and I am running lean, it will always be a number higher than 1, and therefore it will increase the value in the VVE table, and then, since I'm in OLSD will inject more fuel, which should correct the lean condition and go back towards rich, but this hasen't been happening?

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    Something seems off here and its probably contributing to my problem. So I changed it to desired(commanded)/actual(reading from WB), which should technically be right since say your actual WB reading was .9 lambda (lean) you would multiply that calculated quantity (which would be bigger than one) against your VVE table which would then increase the VVE table values which should then increase your base fueling which would then correct it back to stoich. So I tried this but instead of trying to copy and paste the errors to the VVE, I just multiplied the whole portion of the table I was looking at (under about 2200rpms) by about .9 which is about the average value of the math parameter correction factor on the histogram. This would insure it actually made a change given the errors of calculating coefficients and trying to interpolate missing cells and stuff.

    So this made the car read basically that much more leaner at about .72-.73 lambda. So this is obviously going the wrong way, but the really weird thing is I went and smelt the exhaust and I can tell it seems richer, and I can see excess condensation as well (maybe just because it was cooling off and I started it back up).

    Anyway so now I am even more confused. My suspicion is maybe I am getting EQ ratio out of my wideband somehow, even though reading the AEM documentation and using logic it seems like the only thing the AEM wideband will send out to the CAN bus is a lambda value? HP Tuners is also showing, when it reads the virtual module created by the AEM controller/gauge the PID shows "WB EQ Ratio 1 (SAE)" but then right next to it it has units of lambda?? I know you can change the gauge output on the AEM to show you EQ, lambda, or AFR, but according to the documentation it appears this is only what the gauge display shows and doesn't change what it reports on the CAN bus, which is what HP Tuners picks up, it appears that only lambda is reported and you can't change it on the CAN bus.

    Its almost certain to me that the AEM CAN Bus output that I am reading out in HP Tuners is lambda and this is because I can see the value DECREASE when the PCM enables power enrichment, so this would mean that it has to be lambda. Also going over the discussion by Keith from HP Tuners, he states:

    "When describing fuel modifiers, F/A EQ ratio is easy to understand because, increasing the # increases the fuel delivery. An F/A EQ Ratio of 1.2 = 20% more fuel over stoich.

    When we use wideband meters, they report in Air/Fuel EQ Ratio.

    Wait, what? Widebands report values in Lambda.

    Air/Fuel EQ Ratio is the term for the function, who's unit result is Lambda (λ).
    Fuel/Air EQ Ratio is the term for a function, who's unit result is Phi (ϕ)."

    So just because they use the term "EQ Ratio" it still can be lambda since its "Air/fuel EQ Ratio" and not "Fuel/Air EQ Ratio", they both are called EQ Ratio.
    Last edited by cmitchell17; 04-18-2020 at 10:48 PM.

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    I'm really sorry to keep rambling, but something I just thought of that I think would seem like it would cause problems correcting the VVE table. How is bank 1 and 2 accounted for? I know if you are using fuel trim feedback there is an individual right and left bank PID, and then there is another PID that I would assume is the average of the banks? Now I have heard people recommending getting 2 WBO2s one for right and left banks. So If I am in OLSD, I am assuming the right and left injector banks get exact same fueling command right?

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    I think I might have to go against the common thinking and say that virtual torque actually needs to be DECREASED at low airmass values. I have been lowering VT at idle region on both airmass and map tables (and E85 since I have E85) and if there is any effect it has the effect isnt very pronounced. I have zeroed out the immediate idle speed adaptive table in hopes that the ECM would abandon trying to control speed/torque through timing and move the throttle blade which I also increased the values for the predicted tables. That looks like that may have helped in that now instead of the timing signature looking so jagged on the logs now it looks more like a straighter line.

    Capture.JPG

    I have made a math parameter to calculate idle speed error in magenta on top. You can see its somewhat in phase with the spark advance, but if you look at the airmass its definitely completely out of phase with the timing. So when the idle goes overspeed airmass is pulled back and timing is increased towards where it should be. I'm not sure what the behavior is supposed to be when you zero out the immediate proportional speed control gain (I believe in classic "tuning" of a PID controller you are supposed to increase proportional constants until you get oscillation, then start increasing integral control until it damps the oscillation out), but apparently it does this where is seems like there is some major phase lag that will keep the system in oscillation. The good news is it looks like by zeroing the immediate prop constants it has eliminated the jaggedness in the timing which hopefully has made the vibration at idle go away.

    At peak spark timing indicated torque parameters are all negative. I don't understand how engine torque can be negative? unless the torque reserve is factored in or some other torque is factored in? If the delievered engine torque at idle was truly negative the engine would immediately die?

    I would say at this point my VVE is about as good as I can get it. I know this thing can idle better than it does because at colder starts the idle is a lot better almost stock like, and I don't think its just because the idle speed is raised so much either.

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    I tuned a procharged/cammed silverado last week and the single best thing i did was raise the idle rpm to 850, I still had some idle surging and found that the previous tuner adjusted the etc scalar, i put that back to stock and the truck idles perfect now. It took me a good day or so to get it to where I was happy, but those to changes made the biggest difference.

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    Quote Originally Posted by cmitchell17 View Post
    I think I might have to go against the common thinking and say that virtual torque actually needs to be DECREASED at low airmass values.

    I've been saying this for months in random threads lol. I don't know if it is the correct way to do things, but it definitely has an effect on idle and part throttle timing meaning if you lower these values the car will not be pulling timing. Basically lowing the VT tells the car its making less torque so it doesn't try to pull timing out to bring the torque value down. Now this also makes me think we still don't have defined tables that show what the torque limit is per RPM before it starts pulling timing.

    I have also been messing with the Increasing Torque Rate limits in the Driver Demand section and I THINK this also has an effect on how much Torque Management Advance is active on idle and part throttle pedal movement. Meaning if you raise the values, TMA kicks in less just off idle. I was testing this on a ported throttle body and so far have seen lower TMA values when taking off from a stop light vs leaving these tables stock. But I don't have enough yet to say this is actually the case.
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    Quote Originally Posted by ZincGT View Post
    I tuned a procharged/cammed silverado last week and the single best thing i did was raise the idle rpm to 850, I still had some idle surging and found that the previous tuner adjusted the etc scalar, i put that back to stock and the truck idles perfect now. It took me a good day or so to get it to where I was happy, but those to changes made the biggest difference.
    So I agree with a cam there is a certain rpm you can hit to where everything just goes back to normal like magic. I mean this is obviously got to do with larger cams and overlap and combustion stability and EGR effect, but its really surprising that it goes from so rough to almost stock in a few rpms, you would think it would take more rpms. Problem is then you lose the cool sound (which will probably eventually annoy me haha) and then you lose some driveability in parking lots, and unfortunately your car still sounds broken to people who don't know what a cam is haha. Thats kind of my main goal to not be embarrassed by making people think my brand new car is broke haha.

    My problem is I've been chasing all this rough idle issues with a cam, but I don't even know what I should expect with a cam, maybe I can't expect any better idle quality that I already have? I see my wideband jump all over the place sometimes, one day I will take a log to tune VVE and it will be rich, I will correct it and it will be good and normal, the next day its right back to rich, correct it and its normal, then the next day its lean? Makes me think it may be bad combustion stability, I can log misfire counts and see some counts 10-20 in a glance of looking down at the scanner, but I have the same problem, how much is "normal"? We just don't have the right tools to actually really know whats going on, so I could be wasting my time getting myself frustrated because maybe I am getting a false lean condition because of the excessive misfires is letting too much pure oxygen out the exhaust? We just don't have any way to tell.

    I may go revisit idle speed again, but I have another problem, the dynamic testing tools are so buggy you can't use them. Sometimes the idle speed control works, but the idle spark correction bypass (whatever this is supposed to "bypass" I'm not entirely sure) or the timing advance override/control I have never been able to get to work, I am not sure if maybe it doesn't work when the airflow model or torque correction is off by so much or what but I have never seen it do anything.
    Last edited by cmitchell17; 04-30-2020 at 09:42 PM.