Shaking when ICE is Running, NO Check Engine Light

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by iRunfastXC, Dec 18, 2020.

  1. iRunfastXC

    iRunfastXC Junior Member

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    Howdy, fellas! 2nd Gen 2005 with (I know) 350,000 miles.

    Replaced my spark plugs last week, and everything has been running well. Drove to pick up a friend, put her in park, and waited. When we got back out on the road and the ICE started up and I tried to accelerate, the car shook pretty violently, but moved forward.

    I pulled back off the road and drove around the parking lot a bit. On electric, it’s fine. But as soon as the ICE kicks on, the shake comes back. It’s slow, but violent when you step on the gas a little. Somewhat disappears when you hit 25, but returns as you let off the gas and let it idle.

    No knocking sounds or anything like that, oddly enough.

    The bewildering part about it is that there is NO CHECK ENGINE LIGHT.

    Ideas?
     
    #1 iRunfastXC, Dec 18, 2020
    Last edited: Dec 18, 2020
  2. iRunfastXC

    iRunfastXC Junior Member

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    Howdy, fellas! 2nd Gen 2005 with (I know) 350,000 miles.

    Replaced my spark plugs last week, and everything has been running well. Drove to pick up a friend, put her in park, and waited. When we got back out on the road and the ICE started up and I tried to accelerate, the car shook pretty violently, but moved forward.

    I pulled back off the road and drove around the parking lot a bit. On electric, it’s fine. But as soon as the ICE kicks on, the shake comes back. It’s slow, but violent when you step on the gas a little. Somewhat disappears when you hit 25, but returns as you let off the gas and let it idle.

    The bewildering part about it is that there is NO CHECK ENGINE LIGHT.

    Ideas?
     
  3. rjparker

    rjparker Senior Member

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    Never put a female friend in Park. They hate it.

    As for the shaking car, I would read codes. Very likely a misfire caused by plugs, coils or injectors. Misfires will cause the engine to lose sync with the electric motors causing the friction damper to slip. Check engine lights take repeated misfires over a time period.
     
  4. iRunfastXC

    iRunfastXC Junior Member

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    Noted ;)
    Alright, I'll read the codes in the morning and get back!
     
  5. pasadena_commut

    pasadena_commut Active Member

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    Broken motor mount? There would be no CEL because the motor is running properly, it is just bouncing around too much.
     
  6. iRunfastXC

    iRunfastXC Junior Member

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    Hmmm I’ll look into that! Just thought it was odd—I never even turned off the car, just threw it into park for a few minutes.
    Thank you!
     
  7. iRunfastXC

    iRunfastXC Junior Member

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    Alright, update:
    Ran the codes yesterday, misfire cylinder 1.
    Grabbed some new coils, installed them, checked connections, and she ran fine for about a day.

    Today, I was driving a few miles away, and boom. Same problem. So new plugs, new coils, same problem. Just took about a day to manifest.

    Could this be faulty wiring? Just takes some time to fry the coil? I guarantee that tomorrow, it’ll start up fine, run through the warmup cycle, then get rough again. After running it, then shutting it off, the misfire exhibits on the following warmup cycle as well.
     
  8. rjparker

    rjparker Senior Member

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    Might not repeat smooth operation especially if its a coil again. Assuming you once again have a specific cylinder misfire, swap that coil with another to determine if the problem moves. Repeated bad coils can be caused by excessively lean fuel air mixtures, sometimes caused by a failed MAF sensor. Or bad timing.
     
  9. iRunfastXC

    iRunfastXC Junior Member

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    Alright, I know the MAF currently installed is aftermarket. I can swap that fairly quickly. But I would expect other codes associated with the MAF if that was the case.

    If it is timing, what could I look at there?
    Honestly bummed this happened again—and so quickly.
     
  10. rjparker

    rjparker Senior Member

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  11. iRunfastXC

    iRunfastXC Junior Member

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    Update! Good because we know what it is, bad because...

    Anyways, swapped the MAF, coils, and fuel injectors.
    After all that, I finally got the first legitimate sign that it’s what I prayed it wasn’t: a head gasket failure. White, smelly exhaust and coolant in my oil. So sad.
     
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