Continued Misfire and Performance Issues After Repairs – 2012 Prius

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Gsxtron, Jun 14, 2025 at 9:50 AM.

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  1. Gsxtron

    Gsxtron New Member

    Joined:
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    Vehicle:
    2012 Prius
    Model:
    Three
    Hello,


    I have a 2012 Prius with 170,000 miles. The car was experiencing the “death rattle,” so I performed the following maintenance:


    • Cleaned the EGR valve and cooler
    • Cleaned the fuel injectors
    • Cleaned the intake manifold
    • Replaced the spark plugs


    Despite these efforts, the rattle persisted and the engine continued to misfire. Based on your suggestion that it might be a head gasket issue, I went ahead and replaced the head gasket.


    After reassembling everything, I started the car yesterday. While the rattle is now less severe, it’s still present. More importantly, the car now has very little power and shakes during acceleration. I pulled the codes again and it’s still showing a misfire.


    I’m at a loss for what to try next. Any help or guidance would be greatly appreciated.


    Thank you,

    IMG_7493.jpeg IMG_7494.jpeg
     

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    #1 Gsxtron, Jun 14, 2025 at 9:50 AM
  2. adrtho4

    adrtho4 Junior Member

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    2014 Prius
    Model:
    Three
    Is your coolant leaking? Did you check your headgasket?
     
    #2 adrtho4, Jun 16, 2025 at 9:23 AM
  3. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Thoughts:
    Did you get the plugs from Amazon or the mother-ship?
    I'm NOT a Toyota fan-boy and I think that their stealerships could teach politicians a thing or two about life without integrity, BUT their plugs DO tend to be.....THEIR plugs and not some ChiComm knock-off.

    Do a leak-down test to insure that the new HG is OK.
    Cheap to do.
    Definitive.

    Forgive me but I didn't bother to look at the screen shots.
    Are the misfires occurring in just one or two of the cylinders?
    If so, swap the coils around and see if the symptoms change.

    Lastly....(and least likely)
    Compression tests to see if you trashed your bottom end by hydro-locking it before the HG replacement......
    This is a WAG but I'm thinking that a very slightly bent rod will express itself (temporarily) as a shake-rattle-roll and a very slightly reduced compression stroke.
    It's an easy test to do since you're already messing around with the plugs and coils.


    Good Luck!
     
    #3 ETC(SS), Jun 16, 2025 at 11:31 AM
    Last edited: Jun 16, 2025 at 11:36 AM
  4. bisco

    bisco cookie crumbler

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    agree on counterfeit parts. if not, has to be something in the repair.
    make sure all the wiring harnesses are connected properly, no pin corrosion. nothing pinched anywhere
     
    #4 bisco, Jun 16, 2025 at 2:00 PM
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