Engine Rumble at low RPM and Random rough cold starts

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Mysteryos, Jan 15, 2020.

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  1. Mysteryos

    Mysteryos Junior Member

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    Long time lurker, been reading a lot of the threads related to my situation. They usually have one of the listed symptoms, rather than a combination of all of them. Hence, your insight is very valuable on this matter.

    The list of issues is as follows:
    • Uneven idles when charging low HV battery - The ICE will vibrate higher than during a normal drive
    • Accelerating with low RPM at specific speeds (24mph & 37mph) - The ICE will rumble more than usual. The rumble will stop when a higher acceleration is asserted.
    • ICE switch-off speed threshold decreased permanently from 48 mph to 44 mph. This one puzzles me. Scenario is as follows: You are driving at 60mph (ICE on). You start decelerating with regenerative braking. When the speed reaches 44 mph while braking (instead of the usual 48 mph), the ICE will switch off.
    • Random misfire at cold start - The engine will shake violently for 1 second when starting cold. This issue appears randomly and the engine is never switched off during its warm-up period.

    Car Background:
    • Year: Gen 3, 2010
    • Mileage: 78000 miles
    • Driven in tropical climate: 70-86 degrees
    • Hybrid battery: Recently replaced with a brand new one (Tested with Dr Prius, Health 100%)
    • Usual MPG: 55
    • No CEL.
    • No pending codes (checked with techstream)

    Blown Head Gasket Checklist, 5k miles after the above issues manifested:
    • Coolant level stable
    • Oil consumption nil
    • No white smoke from exhaust
    • No milky oil engine cap

    What we've tried to do to fix the issue:
    • EGR cleaning
    • Intake Manifold cleaning
    • PCV valve replacement
    • Fuel injectors cleaning
    • MAF sensor cleaning
    All of the above was done by a mechanic shop in one work day.

    It's my first prius, and I love the car. I'm looking forward to take a head-start on any issue that starts to manifest itself.

    Personally, it feels like the EGR & intake manifold still has some cleanup to attend to. If it all points to that direction, it's time to get my hands dirty.

    Please give us your insights on how to go around diagnosing and fixing the issue.
     
    #1 Mysteryos, Jan 15, 2020
  2. JC91006

    JC91006 Senior Member

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    I don't really like a mechanic to do the "cleaning" associated with the EGR circuit, you have no clue what the cleaning process is. I read all these stories of mechanics charging for work they don't perform, it's part of the industry. To me, if you want it done right, you'll have to do it yourself
     
    #2 JC91006, Jan 16, 2020
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  3. Eddie25

    Eddie25 Member

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    Check spark plugs?
     
    #3 Eddie25, Jan 16, 2020
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  4. tankyuong

    tankyuong Senior Member

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    Egr circuit cleaning should take care of it
     
    #4 tankyuong, Jan 16, 2020
    Grit likes this.
  5. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    Vehicle:
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    Model:
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    ^ This. Seeing is believing. (y)

    Boilerplate text follows:

    The simplest way to see where you're at, is to check the degree of carbon build up in the EGR pipe, a stainless steel connecting pipe between the EGR valve and intake manifold. Watch @NutzAboutBolts video #16 here:

    Nutz About Bolts Prius Maintenance Videos | PriusChat

    Two or three other videos linked there too, for the full cleaning of the intake manifold, full EGR clean, and Oil Catch Can install.

    Good thread:

    EGR & Intake Manifold Clean Results | PriusChat

    Another:

    Oil Catch Can, Eliminate that knock! | PriusChat

    Some tools worth having:

    E8 Torx socket (mandatory)
    E6 Torx socket (optional, but good to have, to remove the throttle body studs from intake manifold)
    3/8" ratchet wrench, regular and long handle, flex head, you can never have enough (or 1/2 plus reducer)
    1/4" ratchet wrench, or 3/8" to 1/4" reducer
    Ratchet extensions: you can never have enough
    Long needle nose piers, straight and bent tip
    Ratcheting 12mm box wrench (optional, but makes disconnection of the EGR cooler from exhaust easier)
    Torque wrench (3/8" and 1/4" both good to have)
    Floor jack and safety stands (or ramps): basically some method to raise front, if you need to take underpanel off, which you may need to, both for access and to recover dropped items.
     
    #5 Mendel Leisk, Jan 16, 2020
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  6. RMB

    RMB Senior Member

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    Everything Mendel and JC said above.

    EGR cleaning you mentioned... is it the EGR Valve? Pipe to intake manifold? EGR cooler? Do you know if your mechanic cleaned it up 100% carbon free... or half a$$ full price job?

    How about fuel qualify in Mauritius? Carbon buildups in combustion chamber, intake valves, spark plugs, etc?

    Ignition coil conditions? Visual inspection and measure resistance?
     
    #6 RMB, Jan 17, 2020
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