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Knocking and rattling noise on low speed 2012 prius

Discussion in 'Gen 3 Prius Technical Discussion' started by Chuba, Aug 16, 2021.

  1. Chuba

    Chuba Junior Member

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    Good day every one.
    My 2012 prius makes knocking and rattling noise when ever the engine starts and I'm on stand still or moving slowly. If I'm speeding the noise stops. I don't have any check engine light on. Scan does not show any issue.

    I have changed the 4 plugs.
    Cleaned the injectors, Intake manifold, throttle body, egr valve all cleaned. After cleaning all these the knocking and rattling sound remains.
    It's comes one at slow speed only if the engine is on and hybrid battery charging. If I match my pedal hard and speeds the sound stops.
    I noticed that this does not happen on cold start. It happens when the car is warned up.
    When I removed the inlet manifold to clean it. I looked inside the engine. I noticed that all the inlet and outlet valves are carbon coated expect the 4 cylinder. I noticed that the 4th cylinder inlet and outlet valves are half inch clean on top.

    Please watch the video link below. It shows exacting what my car does. The video is not mine but exact the same issue.

    Please house what could be the proble and its solution?
    I changed the transmission fluid one and half years ago.
     
    #1 Chuba, Aug 16, 2021
  2. Chuba

    Chuba Junior Member

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    See what cylinder number 4 inlet and outlet valves looks like. U will notice its half inche clean on top. Where as other are black though out.
     

    Attached Files:

    #2 Chuba, Aug 16, 2021
  3. Chuba

    Chuba Junior Member

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    See what cylinder number 4 inlet and outlet valves looks like. U will notice its half inche clean on top. Where as other are black though out.
     
    #3 Chuba, Aug 16, 2021
  4. xliderider

    xliderider Senior Member

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    When you had your manifold off for cleaning, did you replace the PCV valve? A malfunctioning PCV valve could be the cause of the rough running at idle/low speed if it's stuck open, letting in crankcase vapors and loosing vacuum, which affects low rpm performance more than higher rpm performance, when the valve would be open anyway.

    Posted via the PriusChat mobile app.
     
    #4 xliderider, Aug 16, 2021
  5. Chuba

    Chuba Junior Member

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    Thanks for your quick response.
    I removed and cleaned the PCV valve. Forget to add it in the original post. The pcv valve is still as good as new. Checks as normal.
     
    #5 Chuba, Aug 16, 2021
  6. rjparker

    rjparker Tu Humilde Sirviente

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    No video but if it sounds like this it is likely a head gasket since you have replaced the other parts.


     
    #6 rjparker, Aug 16, 2021
  7. Chuba

    Chuba Junior Member

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    Thanks for your response.
    I don't think it's head gasket because my coolant doesn't short and the engine oil does not show any signs of water in it.
     
    #7 Chuba, Aug 16, 2021
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    How many miles on it?

    If 150,000 miles or more, and the Exhaust Gas Recirculation circuit and intake manifold has never been cleaned, I too would suspect head gasket failing. This is happening regularly with 3rd gen Prius (like yours), and very often it's at cylinder one, sometimes cylinder two.

    A leak-down test would help immeasurably, to diagnose determine head gasket condition, and pinpoint where-and-how if it is leaking.

    More info about EGR cleaning in link in my signature.
     
    #8 Mendel Leisk, Aug 16, 2021
  9. rjparker

    rjparker Tu Humilde Sirviente

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    Many people have the same initial response and it turns out to be the head gasket. The coolant leaks small amounts at first and exhaust gasses replace it. Driving like this will make things worse including engine replacement. Other missfire sources like plugs, coil, injectors or stuck open egrs (not clogged) will not quickly clear up and will last long enough to throw codes. A borescope analysis is often definitive as the leaking cylinder will be cleaner than the rest.

    Denial is the first stage of acceptance. In this stage, individuals believe the diagnosis is somehow mistaken, and cling to a false, preferable reality.
     
    #9 rjparker, Aug 16, 2021
  10. wheezyglider

    wheezyglider Active Member

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    Hmmmm.
     
    #10 wheezyglider, Aug 16, 2021
  11. El chingon

    El chingon New Member

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    Have the same issue, no codes. cleaned the intake manifold,
    Cleaned the egr valve
    Cleaned the cooler
    All three items were not to badly clogged.
    Changed the pcv valve
    I did find I piece of the metal catalytic shield loose and it came off, that helped some what but still vibrating at low speed only
    I also changed all four plugs
    Can someone chalk the pics of the cylinder shaft and tell me what you think
    My last resort is to change the injectors
     

    Attached Files:

    #11 El chingon, May 27, 2022
  12. Mendel Leisk

    Mendel Leisk Senior Member

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    How many miles?
     
    #12 Mendel Leisk, May 29, 2022
  13. El chingon

    El chingon New Member

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    150k,
    Today the noise got louder when going slow in heavy traffic.
     
    #13 El chingon, May 31, 2022
    Mendel Leisk likes this.
  14. whazzup

    whazzup New Member

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    Yup, same issue here with my 2013 with 134000 miles. Ended up being the head gasket.
     
    #14 whazzup, Jun 9, 2022
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