Code 300 - random misfire

Discussion in 'Import Vehicles' started by abrad, Jul 28, 2017.

  1. abrad

    abrad Full Member

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    MAKE:Toyota
    MODEL:Corolla
    YEAR:2000
    MILES:132,000
    ENGINE:
    DESCRIBE ISSUE....Been having an issue with this code for the past year or so. The first thing I did was replace the spark plugs, figured it can't hurt, they hadn't been replaced in awhile... Still get the code, but nothing specific that seems to cause it (i.e. - wet weather, temps below zero, etc). I just recently replaced all 4 coil packs, but the code came back. I tossed in some seafoam last week, and all was good. Until today!

    Next up is to start chasing the individual wires backwards looking for wear or rub spots, or possibly a tiny little crack. I've also noticed comments about possibly a low fuel pressure could cause this, or low compression.

    Car has plenty of get up and go, although the wife describes it as "sluggish" at start up - sometimes. It usually starts right up whenever I go out and start it, so not sure what she means. Of course, I get the "look" like I'm supposed to instantly know exactly what she means!

    Anyone else run into similar situations, or have any ideas what else to look for? I'm off Sunday, so guess what I'm going to be doing...
     
  2. nickb2

    nickb2 Wrench. I help when I can

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    A po300 (random misfire) can be tricky to pin point.

    I would sure start by getting some comp readings to rule that right out of the way.

    So, 4 new coil pack, spark plugs, Idea, have you noticed any oil in the spark plug tubes? You may have an oil leak stemming from the valve cover grommetts that have deteriorated the spark plug boots. That is a very common p0300 issue on these engines.
     
  3. abrad

    abrad Full Member

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    Hi Nick. No, I have not seen any oil leaks. When I changed the coil packs last month, everything was dry...

    I'm fairly certain I'm going to be pulling my hair on this one!
     
  4. kev2

    kev2 wrench

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    There are no other codes?
    You are focusing on ignition-
    have you checked fuel pressure?
    Vacuum leaks?
    A scanner showing DATA would give a quick snapshot - ECT, FT's, MAP/MAF, even the o2 voltages will give clues.
     
  5. abrad

    abrad Full Member

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    That's the only code, the other things are what I plan to start looking at this weekend, actually Sunday, when I have a day off!
     
  6. nickb2

    nickb2 Wrench. I help when I can

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    What did you use to pull the code?

    Also, if you are in the habit of driving with low fuel, that also could account for random misfires, especially if everything checks out ok.

    As Kev pointed out, vacuum leaks and fuel pressure could account for that also. A bad coolant sensor also. It may only be missing during warm up. So try to get vac readings and temp reading right at start up on a cold engine and make sure tank is at least 1/4.

    Although a vac leak is usually accompanied by a lean code, I would still monitor fuel trims. Anything +/- 10% is suspect. AT 20%, I would be amazed it hasn't coded rich or lean codes.

    Also, measure resistance of each injector, which is easy to do on these engines. Should be about 13.8 ohms at 68deg f. Fuel pressure should 44-50psi. Cleaning the MAF sensor also may help. A proper cleaning of the injectors and combustion chambers also will help.

    If and when all this is checked out as to be ok, spark fuel, and air, then start suspecting valve clearance or valve timing. I am assuming you will do the compression check before we get to valve clearance and valve timing.

    When doing the injector pressure cleaning, also clean the throttle plate (both sides of plate is preferable) , throttle body and IAC. I am also assuming the air filter and fuel filter are new, yes?
     
  7. nickb2

    nickb2 Wrench. I help when I can

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    That comment of your wife is telling you something that confirms what I wrote above, so checking this engine cold is a must due to that comment. That is probably where the random misfire event is stemming from. After a nights rest, right in the morning is best so the engine has had a full cold night soak. I don't know what temps you are getting down in new york, but they should resemble what we are getting here close to montreal.
     

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