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Thread: Help with IAC please

  1. #1
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    Help with IAC please

    I need help adjusting the iac steps..

    I searched under IAC and found nothing , which I believe is me ... there are plenty of threads addressing my issue I think but cant find them. Just trying to fine tune the idle on a 102mm tb , running a SD tune.
    Getting to much air right now. I want to limit it and be able to do so after logging data instead of just guessing like I plan to do if I can find the file to tweak...

    Thinking about a whole new TB , this one is sticky and always has been. Best tb on the market for performance ? Not looking for FAST knock offs ... I have one...lol Is FAST the best 102 ?

    Ok after looking at a few posts it appears maybe the Holley 105 is the better option. Have never been able to get this current combo to where I am happy it. The TB has always been an issue so its getting pitched into the can.
    Last edited by 79 z28; 09-20-2018 at 07:13 PM.

  2. #2
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    Just ordered the Holley 105 and will set the IAC steps back to stock then properly fine tune it.


    I extracted this from a thread I found .... So I will adj the iac correctly.



    This is actually my first post on here, but I thought I would share some tips on tuning the GEN III dreaded 98 Camaro pcm. I have a 0411 in the mail as I type this, but this is relevant for any IAC car I think. Many people seem to skip the IAC Steps vs Effective Area table, perhaps because the numbers in it are almost impossible to assign a value to. Through forums and other sites and tinkering I came up with a decent way of tuning the IAC steps to reflect more accurate Desired Airflow.

    Changing a cam changes vacuum. Therefore, desired airflow through the stepper motor is not going to be accurate without tuning the steps table. This gives your computer more accurate information and lessens the need to adjust other tables to compensate for the error.

    Step 1. Tune your VE table in SD mode until it is +/- 5 (or less) at idle on your WB

    Step 2. Reduce your IAC steps to 40-60 at operating temp, (lower than this won't hurt). Do this by opening the throttle blade slowly. Remember to reset your IAC motor and TPS after every adjustment. Your idle might get very high while adjusting the blade. Just shut off the car, reset, and start the car. Seems to work on mine, as it will drive the IAC counts down. For 98-02 F bodies, do not exceed .55v on your TPS sensor. It will cause an error. If you still need to bring TPS voltage down, simply loosen the screws and turn it. If required, enlarge the holes SLIGHTLY and remove the centering stub to give more adjustability over the voltage range. The overall goal is to lower the IAC counts in order to give the PCM more control over the idle.

    Step 3. Go to your scanner. Go to Tools>Math Parameters and select a "User Defined" PID under "Maths-user". Now click "new variable" and select "Idle Desired Airflow" (2220.71), then "Dynamic Airflow" (2320.71), and "Idle Air Control Position" (2200). The Equation is: Idle Desired/Dynamic*IAC position. It should look like this: [2220.71]/[2320.71]*[2200]. Name this PID IAC correction.

    Step 4. Make sure you are logging Dynamic, Idle desired, and IAC Control Position.

    Step 5. Create a new histogram graph using your new IAC PID. Under the Column Axis use "Idle Air Control Position." Here's the fun part. For the values, the PCM does not tell you the actual "position" of the motor. It tells you what it thinks it is, i.e., "effective area." This could be anything from 0-310. The fun part is figuring out really what step "310" or any other value actually is since there are only 120 steps. SO, what you have to do is assign "values" to your axis. On the Column Axis you can go by whatever numeral you want, but by 5 seems to work just fine. I go by 2's and even 1's in some areas. Basically you need to enter values from 1-310 in this axis in any form you want, since the motor will "see" any number of them. The more the better. Set your hit count to 25. It should look like this: 1, 5, 10, 15, etc... ...310.

    Step 6. (Optional) Add a TPS and Dynamic AF filter to your log. Something like: [50090.156] < 0.5 AND [2320.71] < 30 This will allow you to log while driving

    Step 7. Do a cold start with the car, and try to avoid stepping on the gas. Mine hates to start cold, so the first few seconds are a wash for me, I just start the scan once the car is running on it's own after a few seconds. It's something I've been trying to fix, but big cam and crappy PCM are not helping lol.

    Step 8. Look at your log, go to your tune file and find the numbers that match the closest from the tune and the log. Example: in your 170 column is says 130. Find the value in your "IAC Steps vs. Effective Area" table that is closest to 170, and change it to 130. Do this for as many numbers as possible, smooth as needed. Interpolate works great for some of the areas here if you don't have values to go off of. You just need to make sure it's a slope and not a mountain range. *NOTE* You should get higher counts when the engine is cold, and lower counts as it warms up (motor closes). Do this for a few days over a few starts. Look at your Dynamic and Desired Airflow values. They should start to come together. Repeat as necessary.

    Step 9. Adjust your RAF (Base Running Airflow) Table. Plenty of write-ups on this, including using the Russ K config file.
    Last edited by 79 z28; 09-21-2018 at 12:04 AM. Reason: Ordered Holley no guessing

  3. #3
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    http://www.silveradoss.com/forums/to...sing-hptuners/

    i used this page to help do my idle tune, read it over and see if its something you want to use
    98 camaro - ls1, turbo , t56, 9" rear, viking coilovers, umi tubular components, weld wheels
    54 chevy 3100 - 5.3, 10bolt, 4 link, coilover setup, custom tubular frame members
    92 miata death cart

  4. #4
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    From my earlier write up that you mentioned, I should say there are a lot of other things to look at before messing with the IAC. You should be able to get it running pretty good by reducing fuel (VE) standard reductions for larger cams, 90%, 80% etc... and then as needed. I am sure you have read most of the forums on this. I still do not understand what the issue is with "getting too much air" would be. Normally that's a good thing, in my book. Just add more fuel lol. In all seriousness, adjusting the IAC is probably about the last thing I tune when tuning for a big cam.

    What you see above is me be very nitpicky, and wanting it to run perfect under all conditions and all that, without having to touch the throttle, in SD mode. If that's you goal, then by all means follow the steps up there and you can actually dial it in. Keep in mind, any adjustments made to VE, RAF, or the TB itself will require this to be redone or verified. Also, it will not solve everything, only compound what problem you might have somewhere else in the tune.

    The big idle killers are Fuel, Spark, Air... In that order. So as you see, still the last step in getting it to idle nice.

  5. #5
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    I got your PM , responded... Yeah I didn't include to much info here either , my bad.

    I was never happy with my idle and the screw holding open the blade always messed with the TPS... The blade was always sticky as well. SO I scotch brighted the edges of the blade, must have taken to much off as I can not get it to idle back down under 1200 rpms.. that's how the thread got started ...lol.. self inflicted wound...lol..

    I honestly was never happy with the TB , it was a FAST knock off.. On someone else combo its probably fine but I got 457 cubes All Pro LSW 7 heads, a 102 , 246/263 .699 lift cam
    its sensitive at low rpm...LOL.... absolutely violent under WOT but I use less than 10% throttle most of the time and that's where the tuning is critical and not working well with the current TB

    Soooo... Holley 105 on the way with the tapered bore.

  6. #6
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    let us know if the holley takes care of your issue!
    98 camaro - ls1, turbo , t56, 9" rear, viking coilovers, umi tubular components, weld wheels
    54 chevy 3100 - 5.3, 10bolt, 4 link, coilover setup, custom tubular frame members
    92 miata death cart

  7. #7
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    Well the Holley and some time logging and adjusting and rinse and repeat ...lol should do it is my hope. I'm sure someone else could maybe have put the time in and got the TB I had to settle down or maybe not, but its going to be fun none the less.

  8. #8
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    forsure, sounds like you have a pretty rowdy engine setup!
    98 camaro - ls1, turbo , t56, 9" rear, viking coilovers, umi tubular components, weld wheels
    54 chevy 3100 - 5.3, 10bolt, 4 link, coilover setup, custom tubular frame members
    92 miata death cart

  9. #9
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    TB gets here tomorrow... Then its go time ..lol

  10. #10
    Senior Tuner cobaltssoverbooster's Avatar
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    i have a 105 straight bore on a 408 n/a stroker your going to like it. easy to setup.
    2000 Ford Mustang - Top Sportsman

  11. #11
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    ok, need a new bracket for the cable but I fired it up and it found its idle very quickly ….. first impression Extremely happy with the Holley. Night and day over the other TB I have.
    I'll pull some logs shortly, have a cable bracket kit on the way. Excited to finally solve some driveability issues at low rpm/speed

  12. #12
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    update : new tb is great, instantly fixed the idle issues. A lot more street friendly as well at low rpms. Doing the VE stuff now .
    I've had a few TB's ...the Holley by far is the best / easiest I've had. Very happy