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Trouble with EGR and Mass air flow 2011 Prius

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by DanWF, Jun 30, 2021.

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  1. DanWF

    DanWF Junior Member

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    My Prius started running a little rough at normal highway speeds and very noticeable around 25 MPH . If accelerating or decelerating it seemed fine. After reading from the internet it seemed likely the problem was the EGR system. I took it apart and it was plugged. I cleaned the cooler with some fine wire and got it opened up pretty well. The valve was stuck and I cleaned it well, so it will move freely. Cleaned the whole system as best I could.
    No improvement. I don't remember any warning lights. After all this I saw that the engine trouble light was on an had it tested. Mass flow sensor was throwing an error. I tried cleaning it with the proper cleaning spray, but no improvement or change. I bought a new one on Ebay and same problems, but also Intake air Temp. PO113 and P0102.
    The problem only occurs (rough running) after it warms up a bit. When cold it runs well.
    At any time during these events I could unplug the MAS, which I believe also contains the Intake air flow sensor, and the car will run well. It gets slightly poor mileage and lacks power at high speeds. It will deplete the battery easily if I push it too much.
    Not sure how to proceed. Any input would be appreciated.
     
    #1 DanWF, Jun 30, 2021
  2. JC91006

    JC91006 Senior Member

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    You should take apart the intake manifold and see if that's plugged up with carbon as well. Hopefully you are not at the "bad head gasket" level yet.
     
    #2 JC91006, Jun 30, 2021
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  3. Mendel Leisk

    Mendel Leisk Senior Member

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    How many miles?
     
    #3 Mendel Leisk, Jun 30, 2021
  4. DanWF

    DanWF Junior Member

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    I have considered doing that. I just don't see how the intake manifold could be so plugged it is causing the mass flow to throw errors, but the car basically runs fine.
    I am confident the head gasket is not a problem. I drive this car 100 miles every day and with the sensor disconnected it just lacks a little power (I can drive 76 MPH, just not 85 like before this started).
    What if the EGR valve is actually bad?
     
    #4 DanWF, Jul 1, 2021
  5. DanWF

    DanWF Junior Member

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    155,000.
     
    #5 DanWF, Jul 1, 2021
  6. Mendel Leisk

    Mendel Leisk Senior Member

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    Cleaning time. Some info in my signature “bad flywheel” (on a phone you may need to click my avatar).
     
    #6 Mendel Leisk, Jul 1, 2021
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  7. DanWF

    DanWF Junior Member

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    I cleaned the intake manifold and installed an oil catch can. I had a lot of oil in the intake. After this I cleared all the trouble codes and it is running pretty well. I am not getting and trouble code, but I still can feel a little miss or something at a steady speed on the highway. I did run live monitor for a few seconds (I don't have an error code device, I use the one at Advanced Auto) and it reported a miss fire on cylinder 4.
    Any ideas on resolving this minor issue.
    Thank you for all the good input.
     
    #7 DanWF, Jul 20, 2021
  8. ChapmanF

    ChapmanF Senior Member

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    There are a lot of potential causes of misfires, and finding them can be subtle, especially when they occur only in certain driving conditions.

    There was a pretty good article on misfire diagnosis in the Second Quarter 2009 issue of Toyota Tech, starting on page 15.
     
    #8 ChapmanF, Jul 20, 2021
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  9. Mendel Leisk

    Mendel Leisk Senior Member

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    Leak-down test is the go-to for head gasket failure. Maybe you’ve dodged it, but still good to verify.
     
    #9 Mendel Leisk, Jul 20, 2021
  10. ETC(SS)

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

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    It may not be a minor issue.
    Were the plugs replaced at 120,000?
    Exchange components between cylinder 1 and 4 and see if the misfire follows.
    As mentioned above.....leak down test.
     
    #10 ETC(SS), Jul 20, 2021
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  11. wheezyglider

    wheezyglider Active Member

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    Humble opinion, based on longtime observation: this is the point in the typical misfire diagnosis where I think it's almost always worth first trying to eliminate the EGR valve (and EGR passages in intake manifold) before checking the headgasket. Because a) it's a known suspect and, b) it's easier/cheaper/more-DIY-able to check.

    (This is for cases where the misfire mainly happens during likely EGR operation -- i.e. when the engine has warmed up enough to enter closed loop, and is under some load but not wide open throttle. That's when the valve and especially the intake manifold are suspect. )

    But yes definitely warn about possible HG failure because leaving that unfixed could lead to catastrophic damage. Start keeping an eye on coolant while checking the easy stuff, that's a no-brainer. Put the HG top of mind, but not top of list is what I'm suggesting. Hope that makes sense.

    And of course since other misfire suspects are still in play, swapping coils e.g. is a worthwhile test.
     
    #11 wheezyglider, Jul 20, 2021
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  12. ETC(SS)

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

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    The OP already did the ERG rinse and set.
     
    #12 ETC(SS), Jul 20, 2021
  13. wheezyglider

    wheezyglider Active Member

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    I got that, thanks. I should have emphasized the phrase *typical misfire diagnosis* because I'm trying to get PC (mostly Mendel :) ) to modify the misfire diagnosis flow chart.
     
    #13 wheezyglider, Jul 20, 2021
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  14. DanWF

    DanWF Junior Member

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    I haven't had time to do any trouble shooting at this point.
    I am really thinking it is a problem with the EGR valve. When I completed cleaning that entire EGR system and cleaning the intake manifold and installing the oil catch can (the intake was loaded with oil), the car was running pretty good. I drive a lot of miles and slowly I have noticed that it is getting just like it was before I started the whole project. It just runs rough at a stable speed with no acceleration. It becomes more pronounced when going downhill. When I accelerate it seems to smooth out. My mileage is doing well (at 60 MPH I will exceed 50 MPG). I should also note that it will run fine until it warms up (at least much better then when it is warmed up).
    If I unplug the Mass Airflow/air temp sensor on the intake the car will run smooth (another reason I don't think it is a head gasket problem), but the mileage and power will plummet.
    Is there any way to verify the EGR valve is actually working? What would happen if I just disconnected it to see how it behaves? Should I just get a new one? I plan to replace the EGR radiator later this fall, it was in really bad shape and although I got it cleaned to the point I can see through most of the holes I know it will plug fairly soon.
    I realize that the head gasket issue is possible, but I would think I would notice froth in the oil. Until I started pulling hoses loose and losing a little antifreeze I had never added any (in over 100K miles, I bought the car with 50K on it).
    When I get a little time I will try a compression test and see if any of the cylinders look off.

    I really appreciate all the helpful input everyone here has given me. Thanks for your time. Hopefully I can get this resolved soon. I really love my little car and want to keep it, but I have to have a reliable vehicle to get me the 50 + miles I drive each way.
     
    #14 DanWF, Jul 27, 2021
  15. wheezyglider

    wheezyglider Active Member

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    For the typical headgasket failure on this car you won't notice anything in the oil or coolant. Instead coolant begins slowly leaking into a cylinder and gets blown out the exhaust. As the leak gets larger, you might notice rougher cold starts. Anyone suspecting this kind of leak should go out in the morning when the car is cold and mark the level in the coolant reservoir with a grease pencil (or whatever). And then check it every morning. (While continuing to look at other possibilities.) If you notice coolant loss over time with rough cold starts, you could pull spark plugs and look for coolant pooled in the cylinders (it will probably be in only one). A $20 USB endoscope helps since the plug tubes are so long.

    Since you know you've got misfiring that is possibly due to the EGR because it happens mostly when the engine is warmed up (and running in closed loop), you can test for it a little more directly than unplugging the MAF (which does also take it out of closed loop and cuts out the EGR, but also takes out the use of O2 sensors and fuel trims). One way is to unplug the EGR valve connector (which will throw a code and turn on the check engine light). If misfiring goes away when you disconnect the EGR valve and comes back when you plug it back in, it's a really good bet the EGR valve itself is problematic or the intake manifold EGR ports are clogged unevenly.

    FWIW a Toyota Master Diagnostic Technician recently posted a youtube video showing a misfire diagnosis technique that uses a putty knife to shim off the EGR valve flow. It looks pretty easy and has the advantage of not telling the computer that your EGR valve is unplugged. (The ECM will tweak its behavior somewhat when it knows the EGR valve is unplugged.) A shim also has an advantage in a case where the valve is suspected of being stuck open (rough idle).

    If you try either of those, let us know how it goes.
     
    #15 wheezyglider, Jul 27, 2021
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