Very rough idle, several DTCs, odd smelling exhaust

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Bigger, Apr 16, 2017.

  1. Bigger

    Bigger Junior Member

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    We bought the car 18 months ago from a used car dealer, who took it in trade from the world's most perfectionistic maintainer of Prii- two hundred K in Maine and there was not a single spot of rust.
    The car has idled roughly before, usually at startup, but always recovered. Not this time.

    While driving in light traffic a few days ago, the Prius started bucking, losing power, and idling really roughly. We limped it home (half a mile) and dusted off the VTC cable and Techstream 9.

    Techstream gave me P0300 (intermittent misfires), P0303 P0304 (misfires in cylinders 3 & 4)- no news there. I also got P0A0F.

    P0A0F seems to be a gunked up throttle body, so I removed the air cleaner box and MAF and carefully used a throttle-body-cleaner-dipped toothbrush and lint free paper towels to clean the plate and the throat. I observed that there was a slight oily slick at the bottom of the throat- not sure if that is cause for alarm.

    I reassembled everything, replaced the air filter (since I was in the neighborhood anyway- it showed some Texas dust but not much), and started the car again. Same result. I noticed, since I had the windows open, that the exhaust smelled off, like a very rich mixture. If I just touch the throttle (Techstream says around 1500rpm) the idle smooths out quite nicely and I don't smell funky exhaust, but that only lasts for a few minutes before the engine decides that it would rather idle at its normal speed and starts stumbling and coughing again.,

    Other threads mentioned the 12v battery as a possible culprit. I could not see a date code on the battery, and my VOM is sixty miles away, but Techstream assures me that the battery was putting out 13.8. I put it on a trickle charger for a few hours just to be sure. No change.

    I haven't yet checked the MAF; not sure how I can check it, apart from just visually noting that it exists.
     
  2. hchu1

    hchu1 Member

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    Here is a Youtube for your MAF, recommend muting music:


    I used a qtip and 70% isopropyl alcohol, because that's what I had, why spend if you don't have to? Just be really careful using the qtip on the bulb, it should be amber in color translucent when done. It will likely look somewhat gray black in color prior to cleaning. Good luck.

    Note: It is recommended to use MAF spray, my own experience was the above alcohol and qtip, the sensor is working fine 3+ years strong. YMMV.
     
    #2 hchu1, Apr 16, 2017
    Last edited: Apr 16, 2017
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  3. dolj

    dolj Senior Member

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    Do not use a qtip on the MAF sensor. Spray only MAF specific cleaner on it and let it dry off.
     
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  4. andrewclaus

    andrewclaus Active Member

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    Ditto, get a spray can of MAF sensor cleaner.

    Also some injector cleaner.

    The 13.8V you got was the charging voltage, not applicable here. The battery should be checked, but it's probably not causing the problems you're seeing here. You can use the car's MFD in lieu of a VOM. Search on this site for process and thresholds.

    What condition are the plugs and coils in? While you're there, change the PCV valve.

    Don't worry about the oil slick, they all do that.
     
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  5. Prius Jas

    Prius Jas New Member

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    Some good info there.

    Swapping the coils 3/4 one at a time with no.s 1/2 could show if you have an issue there also. Easy check.
     
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  6. Bigger

    Bigger Junior Member

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    I'll pick up MAF cleaner and injector cleaner tomorrow. Fortunately the parts store is an easy walk from here.

    Plugs are a year old. I haven't pulled them yet. With the P0303 and P0304 I assume that cylinders 3 and 4 will show... what? Fouling?

    Coils are from before we owned the car. Is there a way to test them that doesn't require special tools or more than modest skill?
     
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. DTC P0A0F is logged by the hybrid vehicle ECU and just means the engine failed to start. Exactly why is not specified.
    2. Yes, remove the spark igniters for cylinders 3 and 4 (the cylinders closest to the inverter) and inspect them. Look for flaws such as cracks in the plastic body, rust deposits on the rubber insulator, corrosion on the electrical connectors. If there is any doubt, replace the suspect igniter.
    3. The way to test the spark igniters other than a visual inspection is to move the suspect igniter to another cylinder and see if the misfire DTC moves to that cylinder. If it does that is good proof the igniter is bad.
    4. The spark plugs should be removed for inspection. If the porcelain insulator has any rust deposits (from water dripping into the spark plug well) then replace the plug. I hope you installed the correct NGK or Denso iridium spark plugs only. If not, this would be a good time to get rid of the inferior plugs.
    5. Remove the MAF sensor for cleaning by unscrewing the two little screws that hold it to the air cleaner housing. What needs cleaning besides the amber bulb is the two very thin and delicate wires. That is why you do not want to use a Q-tip or anything that would touch the sensor.
    6. If you were really desperate and could not afford or locate MAF sensor cleaner spray, it would be better than doing nothing, to dip the sensor into clean isopropyl alcohol. However that is to be discouraged if the correct MAF sensor cleaner spray can be located.
     
    #7 Patrick Wong, Apr 16, 2017
    Last edited: Apr 16, 2017
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  8. Prius Jas

    Prius Jas New Member

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    There will be threads on here that will show you the testing procedures for coils I'm sure. Replicating heat and moisture variables during a bench test would be harder to do. Swapping the coils with the known good units one at a time should move the fault if the coil is the issue. Ensure you check all plug connections for cleanliness/security and the coil pack seal is there and in good/clean condition also.

    Unsure what the weather is like in your part of the world but heavy rain and deep puddles don't help either, I had the same faults up when a driver tried to use a car as a submarine. I couldn't work out why there was so much moisture in the spark plug cavities until I put it on the hoist to do a routine brake check and the spare tire well blanking grommet wouldn't stop dripping. By pushing on the grommet I drained a half full spare tire cavity and had my answer.
     
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  9. Prius Jas

    Prius Jas New Member

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    Patrick obviously types faster than me......
     
  10. Bigger

    Bigger Junior Member

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    High desert. 70ish degrees (Farenheit, natch!), low humidity, no rain for months. Dust is a problem here, hence the replaced air filter- the intake side of the air cleaner box was clean enough to eat from and the filter could have gone months more but I figured that I was thinking about it now.
     
  11. edthefox5

    edthefox5 Senior Member

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    How many times has the engine showed very low oil on the dipstick?
     
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  12. Bigger

    Bigger Junior Member

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    Not at all, that I remember. It is on the low end of acceptable (about 1/4 of the way up between the two holes) right now.
     
  13. KSlauson

    KSlauson Junior Member

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    Consider cleaning or replacing the injectors, especially 3 and 4.

    Nexus 7 using PriusChat mobile app
     
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  14. Beachbummm

    Beachbummm Active Member

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    If the smell is like rotten eggs the catalytic converter is going bad. Oil in the intake seems to be common I and not a sign of damage. I'd change the PVC value and avoid oil additive s... As my car has gotten older I have changed the oil more often.

    I hate gas stations so I bought a Prius
     
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  15. Bigger

    Bigger Junior Member

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    Misadventures, chapter two!

    I picked up some pour-in injector cleaner, some MAF cleaner, and a quart of oil.

    I topped up the oil, which was above the bottom hole in the dipstick but not by much- added half the quart. I added the injector cleaner to the tank as well.

    I redisassembled the air cleaner box, removed the MAF and cleaned it with the spray. Once I put everything back together, the problem was worse! Now I can't get a decent idle even by feathering the throttle. I don't even want to run the gas engine for long enough for my laptop to connect to the Prius and diagnose this, if I can avoid it. The poor car sounds terrible,
    • Since the MAF was the only component that I molested that should have this kind of effect, I'm suspecting that the MAF went south on us. The over-rich exhaust smell could certainly come from from the MAF misreporting airflow, leading to a very rich mixture.
    • Since two cylinders are missing, it would require two plugs or coils to die at once- possible but unlikely.
    • It could be the fuel pump- if the fuel 'starts' at cylinder 1 then it would make sense that insufficient fuel would reach 3 and 4 but I can't see how feathering the throttle would have solved that. Also, replacing the entire gas tank is way to much pain and silver to do without a lot of certainty.
    I'm somewhat handicapped by having my tools spread between two properties. Naturally my socket set with spark plug sockets is not nearby, so I can't check the plugs until I either walk sixty miles out into the desert or fix this catch-22 problem.

    So, I'm going to throw a few twenties at the problem and replace the MAF. I'll report success or despair tomorrow.
     
  16. Bigger

    Bigger Junior Member

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    The smell is like starting an old carbeurated/choked car on a cold morning. Incompletely burned gasoline. I'm glaring suspiciously at the MAF right now, since if it want out I could understand the car having a terrible mix (too rich).
     
  17. edthefox5

    edthefox5 Senior Member

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    yes that sounds like the maf is bad but it would throw a code also.

    Be aware under the air cleaner box is a throat clamp 10 mm bolt. If not tightened you will have unmetered air sneaking by the maf and it may not run right.
     
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  18. edthefox5

    edthefox5 Senior Member

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    Btw, fuel doesn't "start" at cyl number 1. Your assuming the car starts in its firing order.
    It starts at whatever piston happens to be on compression stroke. Then it continues to fire in its firing order.

    There have been a few posts about bad fuel pump. You can rent for free a fuel pressure gauge at most parts stores. Just need to leave a deposit.
    I suggest you go to toyotatechinfo and rent a 3 day subscription to the service manual. Get the printer ready and drill down to the misfire section and follow the troubleshooting tree.
     
    #18 edthefox5, Apr 19, 2017
    Last edited: Apr 19, 2017
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  19. andrewclaus

    andrewclaus Active Member

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    I believe you need to install a test port on the Prius to measure fuel pressure, so it may not be "plug and play."
     
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  20. Bigger

    Bigger Junior Member

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    This would tend to lean the mixture out, right? More air than the MAF sees going into the same amount of fuel?

    I've tightened that bolt, though I can't see what I am doing there. The air filter box is sitting squarely and securely on top of the throttle body, anyway.
     
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