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Thread: Idle surge after cam and intake install

  1. #1
    Tuner in Training
    Join Date
    Apr 2016
    Location
    Iowa
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    23

    Idle surge after cam and intake install

    Good Morning, I've had some issues getting the idle worked out on a 408 LS we just put together. The car has a 260ish duration cam with 243 heads, and fast 92 intake. I now have it idling well enough where it doesnt seem to want to die when you let off the gas and roll up to a stop sign, but it sill surges and idles too high. Any suggestions? Idle scan and tune below.

    Thanks for the help!
    BlakeBeau Regal 408 1.0.hptRegal 408 Idle tune 1.2.hpl

  2. #2
    Senior Tuner
    Join Date
    Jan 2013
    Location
    Hawaii
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    2,101
    Doing the high idle spark thing is just to get it starting and running. Add to your base running airflow, and pull timing out of your idle spark(once you can) until the over/ underspeed spark control calms down. Watch IAC position to not max it out.

    Then take a log with adapt STIT/LTIT.
    Start with a warm car at your commanded idle RPM. with AC off using the scanner vehicle control, start commanding a spark ~5* less than what you found made your idle adaptive calm down. Go up 1* at a time in 15 second increments until you are near 40-45*. This will show you the spark advance your STIT likes and what spark produces the most vacuum. No need to go much higher that that spark advance.
    The spark the STIT like will be what you want in your idle table. The spark that produces the most vacuum will be the one you want in your base tables.
    The spark STIT wants will be directly related to what airflow values you have in base running airflow. So if you want more idle spark to have them closer to base values, lower the airflow. If you want less, raise the airflows.

    Then take another log doing the same thing, using the scanner vehicle control start at 800 RPM go up in increments of 200 RPMs pausing for 15 seconds at each step. This will get you the spark needed to achieve idle at that RPM and airflow. It will give you a good idea of how to blend idle spark into the higher base table spark through the increase of RPM. Also how to return to idle nicely(lower spark values in the lower airmasses), be careful not to cause too much startup flare, and use the startup flare control table to counter act it.
    Last edited by murfie; 09-22-2020 at 03:01 AM.

  3. #3
    Advanced Tuner
    Join Date
    Aug 2010
    Location
    Detroit, MI
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    926
    It isn't in idle mode. Dial back the throttle screw..

  4. #4
    Senior Tuner
    Join Date
    Jan 2013
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    Hawaii
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    There yah go, get it on the IAC valve and off the screw.

  5. #5
    Tuner in Training
    Join Date
    Apr 2016
    Location
    Iowa
    Posts
    23
    If I set the idle screw in anymore I cannot get it to idle without the IAC being in the 200's which I believe is a bit more than we want it to be. I reset TPS but for some reason still showing .8%. Do I need to drill a bigger hole to keep the throttle blade closed and not have the IAC motor at that many clicks? Its a Nick Williams throttle body with no modification to the idle hole. I will pull timing to try to get it to stop over correcting, should I mess with any of the adaptive idle protocals or throttle follower/cracker?

    Thanks for the help guys...Idle tuning has proven to be a lot bigger hassle on this car than I was expecting.