Strange idle, jerking idle, spark plugs breaking up

Discussion in '2005+ Mustang GT 4.6L Tech' started by 3vEvan, Sep 7, 2020.

  1. 3vEvan

    3vEvan Junior Member

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    hi i have a 2006 mustang gt with an auto trans. my mods are an edlebrock eforce kit with a 3.5 pulley, hot rod cams, offroad hpipe, borla ataks, BA5000 MAF, msd master blaster coil packs, autolite HT0 spark plugs, 39lb injectors, walbro 400 fuel pump and 4.10 gears.
    I've been having issues for some time now where sometimes on start up the car will have a jerking idle varying between like 200-300 rpms and it'll rock the whole car. Sometimes it will idle fine and occasionally miss or start struggling to maintain idle and the engine will start shaking real bad may or may not come back up and if I rev it up itll idle back down and die... while driving it seems fine 90% of the time other than when the car downshifts and I give it gas the plugs will start breaking up real bad or when im slowing down itll idle weird till it adjusts. It pulls great at WOT ive been to the track and it runs high 11s. I've cleaned the maf/throttle body, I've changed to multiple TPS sensors, and done KAM resets but none of that seemed to work and I dont wanna buy a bunch of stuff to replace if its not the issue any feedback is appreciated. Thanks!
     
  2. Juice

    Juice forum member

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    You need to datalog the issue to see what the PCM is seeing/doing and why.
     
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  3. Am Speed

    Am Speed Junior Member

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    3vEvan - out of curiosity, what did you gap your Autolite HT0 plugs at? I ask because I also have a 3v and getting read to install the eForce kit soon. I'm seeing folks recommend to gap them at .032 to .035 rather than the factory .045 gauge. I've read that the factory gap can lead to the rough idle you are describing - here: https://www.modularfords.com/content/208-How-To-Gap-Autolite-HTO-Spark-Plugs
     
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  4. stkjock

    stkjock ---- Madmin ---- Staff Member Administrator Super Moderator S197 Team Member

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    gap should not effect idle with a blower, at peak boost yes, you gap down to avoid spark blowout. you want to run the largest spark plug gap possible before you get spark blowout.
     
    Last edited: Sep 9, 2020
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  5. 07 Boss

    07 Boss Senior Member

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    Have you pulled the plugs and looked at them? Reading spark plugs is old school but its how we used to do it.
     
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  6. 3vEvan

    3vEvan Junior Member

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    I have not pulled them out yet but im strongly considering it now

    I dont remember what I gapped them to honestly
     
    Last edited by a moderator: Sep 9, 2020
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  7. AndrewNagle

    AndrewNagle forum member

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    Could take this a couple of ways
     
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  8. svanur

    svanur Junior Member

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    I had the same issue with the autolite ht0 plugs so i stopped using them 2 years ago and switced to brisk 3VR12S for when i am using blower+nitrous and 3VR14S if not using nitrous. After swapping the plugs i have not had any of the issues the ht0 plugs generated. I gap the 3VR12S at 0.28 and 3VR14S at 0.32.
     
    Last edited by a moderator: Sep 13, 2020 at 11:18 AM
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  9. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    I've gaped my HT0 plugs at .032 and currently gap them at .030 as recommended for my current JDM tune. Needless to say, I've never ran across any rough idle nor bogging or jerking issues. What you read about the factory gap of .045 leading to rough idles on a FI application is in fact accurate, as the maximum gap for an FI application should be no more than .035 Therefore, if your not sure what your plugs are gaped at? then it would be in your best interest to pull/check them.

    If you had idle issues while running Autolite HT0 plugs? it's more than likely they weren't gaped between .030-.035 as required when running FI applications.
     
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  10. svanur

    svanur Junior Member

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    They were all gapped at 0.32 and that was double checked and still it happend. So i switched to brisk. I have gone through atleast 4 sets of HT0’s where this has happend not one issue with the brisk.
    Might just be my luck
     
  11. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    In that case, I just may have to consider Brisk plugs for my next set, especially knowing they're a one-piece design spark plug :waytogo:
     
  12. Doug Huggard

    Doug Huggard Junior Member

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    A smaller plug gap would not matter at idle as the engine is in a state of vacuum and not blowing out spark. Your issue is happening at idle so I would start by checking for vacuum leaks. If you have a vac leak post MAF, it will cause idle issues because un-metered air is entering the engine and will cause a misfire or small rpm bump (how severe is dictated by the size of the leak). How do you have your pcv system setup?
     
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