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Thread: Hanging rpm/idle, new manifold and throttle body

  1. #1
    Potential Tuner
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    Apr 2021
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    Question Hanging rpm/idle, new manifold and throttle body

    Hi everyone, this is my first attempt at my own tune. Car was running fantastic prior to the new mods. I added. So far the car runs great I adjusted my maf and tuned for spark knock. But I cannot figure out how too fix the hanging rpm/ idle issue. After letting off the gas my car struggles too decelerate and in neutral my car hangs at around 1150rpm until around 5mph then it drops slowly drops too my set idle. I?ve been having to apply lots of brake pressure too stop. Any recommendation would be great. Read some forums and some YouTube videos about throttle cracker ect, but nothing specific too fixing gm gen 4 issues specifically.

    My car is a 2009 ls3 corvette manuel
    Previously tuned Mods are:
    Stage 3 tsp cam kit
    Slp Blackwing intake
    1 7/8 catless headers
    3in catback exhaust
    Stock throttle body
    Stock manifold
    Stock injectors

    New mods:
    Fabricated long runner intake manifold
    102mm throttle body

  2. #2
    Tuning Addict blindsquirrel's Avatar
    Join Date
    Apr 2017
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    Meridian MS
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    Throttle Learn

    Without Scan Tool - Learn Procedure

    Important: Do NOT perform this procedure if DTCs are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.
    Start and idle the engine in PARK for 3 minutes.
    With a scan tool, monitor desired and actual RPM.
    The ECM will start to learn the new idle cells and Desired RPM should start to decrease.
    Ignition OFF for 60 seconds.
    Start and idle the engine in PARK for 3 minutes.
    After the 3 minute run time the engine should be idling normal.

    Important: During the drive cycle the check engine light may come on with idle speed DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.
    ⇒ If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.
    After the drive cycle, the engine should be idling normally.
    ⇒ If the engine idle speed has not been learned, turn OFF the ignition for 60 seconds and repeat step 6.
    Once the engine speed has returned to normal, clear DTCs and return to the diagnostic that referred you here.

  3. #3
    Post your tune.

  4. #4
    Senior Tuner
    Join Date
    Nov 2006
    Posts
    2,608
    Quote Originally Posted by Sean1m View Post
    Hi everyone, this is my first attempt at my own tune. Car was running fantastic prior to the new mods. I added. So far the car runs great I adjusted my maf and tuned for spark knock. But I cannot figure out how too fix the hanging rpm/ idle issue. After letting off the gas my car struggles too decelerate and in neutral my car hangs at around 1150rpm until around 5mph then it drops slowly drops too my set idle. I?ve been having to apply lots of brake pressure too stop. Any recommendation would be great. Read some forums and some YouTube videos about throttle cracker ect, but nothing specific too fixing gm gen 4 issues specifically.

    My car is a 2009 ls3 corvette manuel
    Previously tuned Mods are:
    Stage 3 tsp cam kit
    Slp Blackwing intake
    1 7/8 catless headers
    3in catback exhaust
    Stock throttle body
    Stock manifold
    Stock injectors

    New mods:
    Fabricated long runner intake manifold
    102mm throttle body


    Have you looked into the ETC scalar? Most throttle bodies require this to be changed. A lot require it to be maxed out. What brand throttle body?
    Tuner at PCMofnc.com
    Email tuning!!!, Mail order, Dyno tuning, Performance Parts, Electric Fan Kits, 4l80e swap harnesses, 6l80 -> 4l80e conversion harnesses, Installs

  5. #5
    Potential Tuner
    Join Date
    Apr 2021
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    6
    It’s a sharp performance tb, I have not looked into etc scalar yet. How would I know what value too max it out? Is there some sort of a standard value for a 102m tb? I will post my tune momentarily.

  6. #6
    Senior Tuner
    Join Date
    Nov 2006
    Posts
    2,608
    8192 is the largest value you can input. Just try that.. Worse that can happen is it will idle low. There is no standardized value for a 102 throttle body.

    I'll tell you something though.. There is a lot that goes into a throttle body. Flow is not the issue but low speed performance is. I've never heard of that brand before so I looked it up. For $199 for a ETC throttle body I don't know what type of quality your going to get there. This might introduce quite a lot of tuning issues and at best you are looking at 2-3 rwhp over the factory throttle body with your setup.


    To anyone else reading/ contemplating a throttle body. Even the wildest NA setup will barely pick up anything on the dyno with a 102,103, etc over a stock throttle body. Same goes for turbo setups.

    The cars that this makes a huge difference on is positive displacement blowers.. Whipple, magnacharer, LSA,etc.
    Tuner at PCMofnc.com
    Email tuning!!!, Mail order, Dyno tuning, Performance Parts, Electric Fan Kits, 4l80e swap harnesses, 6l80 -> 4l80e conversion harnesses, Installs