Come along with Eric O. as we have a look at this 2005 Subaru Legacy 2.6 SOHC that has an intermittent problem of a P0300 accompanied with poor running, no power then all of a sudden it will run good and may not act up for another month.However it is acting up at this time so let's see if we can get to the bottom of this mystery! -Enjoy
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50 thoughts on “Subaru intermittent misfire – p0300”
  1. Avataaar/Circle Created with python_avatars WNX Rumbler says:

    i came tov the conclusion that my 2003 forester needs a coil pack a while ago and put my parts car one on it. it would loose power going long drives, up hill sometimes and all the sudden it just has a major misfire in one cylinder now. i put sparkplugs into it and didnt help, new wires but nope, threw on a fuel filter and injectors but not that either. so i am putting new 02 sensors on it cause i figured the cat was clogged since it was red hot a while back and it only has a p130 code but has set for almost a year now just couldnt figure it out. if the dam 02s dont work im getting a new coil pack and if that was it im going to be happy and pissed haha but either way everything else was done haha fml. dosent help the other parts car had the same peoblem and why the guy sold it!

  2. Avataaar/Circle Created with python_avatars Larry Ericksen says:

    Is it a valid conclusion that oil leaking onto one or more spark plugs, is the cause of an intake backfire under load?

  3. Avataaar/Circle Created with python_avatars Z DJ says:

    Hi Erick
    Making great videos with Subaru and other cars ,doin fantastic job as well .
    Im owner of Subaru Ej253 Forester , 2.5L
    Having light isue when is cold in morning does misfire
    And sometimes when Revs between 1.5 k and 2.k does miss link when I let clutch ,and when is warm not missfireing
    Changed new :
    Ignition coil , map sensor , spark plugs ,New cableS as well changed throttle body / used one
    And when i scan with odb tool meter , no codes showing either

    Any opinion ?
    Big hello from downunder
    NSW Australia

  4. Avataaar/Circle Created with python_avatars John Weiland says:

    I always drove it till it's dead. Easier to troubleshoot but tow bill and broken car laughing at me and not driveable.

  5. Avataaar/Circle Created with python_avatars kfl611 says:

    Won't throw parts at it, as it is the customers money? the subaru just threw $3,000 parts on my car and $2,700 labor – and wanted to add in an additional $3,000 catalytic converter on to the deal…………my car was not worth all that money – I guess they were trying to nudge me into buying a new car……………nope…….I didn't win the lottery, not doing it, no matter how nice the 2021 cars are. The kids are great !

  6. Avataaar/Circle Created with python_avatars Ozzy Krahn says:

    woopty doo for my subaru

  7. Avataaar/Circle Created with python_avatars _ Fundaemental says:

    Just found this channel. Bought a 99 forester three days ago it crapped out on me, shimmy shaking losing power. So here I am sitting at work watching YouTube lol. Keep up the good work. Really like the detail in the video. Keep up the good work.

  8. Avataaar/Circle Created with python_avatars WouterB76 says:

    SMA be like, no parts cannon allowed !

  9. Avataaar/Circle Created with python_avatars Labrador McGraw says:

    I've said it before; I'll say it again: you just cannot beat the South Main Auto channel. We come for the knowledge, we stay for the skills, but we return for the company. Unbeatable.

  10. Avataaar/Circle Created with python_avatars Dependable Auto Truck says:

    did u use a attenuator on this application could see where you probed coil but didnt see other connection

  11. Avataaar/Circle Created with python_avatars juicer52 says:

    P0303 on my 08 Outback. Happens after car has been sitting in a very damp garage. Car bucks until it warms up and then some. Pulled #3 wire and the spark plug tube had moisture on it. Dried it off and let the plug well dry out before reassembling and it runs fine now. Would you use dielectric grease (or some other substance?) along the top neck of the tube where it seats into and "seals" up against the engine to prevent moisture making its way down the tube?

  12. Avataaar/Circle Created with python_avatars Dan falley says:

    Awesome job as always

  13. Avataaar/Circle Created with python_avatars Gabriel Quintino says:

    After battery reset or deleting faults, turn the ignition to the on position for 10 seconds before cranking. It allows the throttle body to learn position and prevent the extended crank

  14. Avataaar/Circle Created with python_avatars VVL says:

    If I was going to try to find a shop that operates as good as Eric, How would I know they are as competent????? Help me?

  15. Avataaar/Circle Created with python_avatars xMG says:

    I wish every mechanic was as honest as you

  16. Avataaar/Circle Created with python_avatars xMG says:

    My 06 legacy gt's engine started to shake when i went to accelerate when i was on the highway i was going like 60 and i tried accelerating more and it started to shake then the CEL blinked like twice then went away and then came on later, what could this be?
    Also my brother checked the coils and one of them was kinda cracked, do you think it couldve been the coil?

  17. Avataaar/Circle Created with python_avatars Tim Klein says:

    good video; honest shop; must have a lot of business !!

  18. Avataaar/Circle Created with python_avatars chippyjockey says:

    I bet it's crank sensor.
    I know people will say they ether work or don't.
    But I've changed alot of crank sensors and it's fixed misfires.
    I guess the sensor gets a hair line crack that is fine till everything warms up and then it expands and interferes with the signal .
    Especially as crank sensor times the spark. 😎😉

  19. Avataaar/Circle Created with python_avatars Natedoc808 says:

    I finally tracked down my misfire mishaps! Two problems: poor connection in ECM to manifold harness connector which cleaned up with contact cleaning and extra ooomph plugging it in….. after that the Cyl 3 misfire continued: Ohm-Ed it out and found open ECM wife in the manifold side of the harness. Now to isolate to wire vs plugs. I’d have loved to turn you loose on my 02 WRX wagon on this one.

  20. Avataaar/Circle Created with python_avatars HypnoticSuggestion says:

    Thank you so much. I am having this identical issue, on a 04 Impreza Outback Sport 2.5 SOHC, same thing.

  21. Avataaar/Circle Created with python_avatars chrisdash83 says:

    Hey Eric, I've got a 2005 Toyota Prius II with 150k miles, it runs fine and no MIL, but it has a P0301 (sporadic). So the issue is limited to cylinder 1. Am I right to assume its most likely spark plug 1, ignition coil 1, bad wiring for cylinder 1 ignition, or a worn out (not compression) cylinder 1? Vacuum leaks, bad MAF, etc should result in more randomly spread misfires, right?

  22. Avataaar/Circle Created with python_avatars Derrick Odyes says:

    uga duga a naper croil might last once around the block

  23. Avataaar/Circle Created with python_avatars William Whitehead says:

    And all wires

  24. Avataaar/Circle Created with python_avatars William Whitehead says:

    Sparks need replacing on all cylinders

  25. Avataaar/Circle Created with python_avatars mark lavrack says:

    Same thing happening with my 2002 Buick regal 3800 non supercharger. Intermittently random misfire code 0300. Very difficult to diagnosis when engine runs fine for a month then once in a while looses power then regains power within ten seconds. I just don't know how to tackle this. I would rather not wait to be stranded. Any suggestions?

  26. Avataaar/Circle Created with python_avatars GNX157 says:

    Seeing the new wires, I wonder if the old ones on that side were open and causing the coil to be overworked and get overheated causing damage to it internally.

  27. Avataaar/Circle Created with python_avatars Kevin Keim says:

    Hey Eric I work on Subaru's also if u can't duplicate the miss spray water from a squirt bottle on the coil usually if it's bad it will act up right after. No need to break out the Pico.

  28. Avataaar/Circle Created with python_avatars rmblwgn says:

    Gosh darnit I just Did a Vf39 turbo swap onto my 2005 ej205 w/pink injectors and sti intercooler and now I have p303 misfire. Car idles rough and has no power, turbo will barely spool before 4k rpm. I replaced turbo inlet hose as oem one sucks and it was falling apart so I thought that would solve problem(massive vacuum leak) but same problem persists.. Anyone have any ideas. Problem was not present before swap.

  29. Avataaar/Circle Created with python_avatars Toasty says:

    My '06 Forester had a similar misfire problem but it would happen after big temperature changes. Found out the rubber around the spark plug wires was dried out and allowing moisture in causing the misfire. $4 tube of electrolytic grease and it runs good as "new"!

  30. Avataaar/Circle Created with python_avatars daveogarf says:

    One! Two! Ugga-Dugga-CUE!

  31. Avataaar/Circle Created with python_avatars Mike N says:

    Just replaced the ignition coil on my ‘08 Forester, had rough running and code P0302. Coil looked a little crusty on wire 2 post, in fact the wire broke off. I don’t have a fancy scanner so I took a chance and replaced it (and plug wire) with parts from the junkyard. Figured I could buy 20 coils used for the price of one new. Anyway, took the car out for a toot, problem solved. Thanks Eric!

  32. Avataaar/Circle Created with python_avatars RC Hobbyist Extreme says:

    I had a 1982 Mercury Lynx, brand new about 500 miles and the coil was leaking oil. I took it to the garage under warrenty and the service manager told me that because it was still working, they might not be able to cover it. I blew up at him and told him so its NORMAL to leak and they ALL are supposed to leak? I told him I wanted to see his manager . What an IDIOT! The manager looked at him and said " REALLY?" JUST REPLACE IT! I had it out with that service manager again when the exhaust fell off a week later. It was defective. At first he started his crap and I said " Really? " Just like the Manager said for the coil. They replaced it. A month later I got a RECALL on it for the exhaust being defective. That was the same model that was recalled for bad headbolts. Mine never developed an issue so I never took it in. Apparently, the headbolts were supposed to stretch but didnt, so many Escorts were developing blown head gaskets or the head bolt were snapping off in the head. I put about 200k on that little car before trading it. I owned two other Escorts after that. I actually had 280k on our last Escort. I took it in to the dealer and he said it had hardly any compression left and was blown away we had put that many miles on an Escort. I had changed the timing belt twice in its life time, did countless brake jobs and many other things but that kept that Escort running up till the end of its serviceable life. The mechanic was impressed that looked at it. Came out to tell me he had never seen an Escort with that many miles and well maintained. Hey, I will take those compliments all day long.

  33. Avataaar/Circle Created with python_avatars ejmagras says:

    Hi Eric O. I have a 97 Subaru outback and it only misfires on cylinders 2 & 4 when the temps are below 35 degrees. Misfires seems to go away during the spring summer and fall. Any thought?

  34. Avataaar/Circle Created with python_avatars Derrick Quintal says:

    Also another thing to always check on these Phase2 Subaru 2.5s is the spark plug tube seals. Leaking ones can cause oil to get in by the plug and cause intermittent misfiring. I'm sure you already know this though.

  35. Avataaar/Circle Created with python_avatars Timothy Hartzell says:

    My personal preference is to know at least 99% that my diagnosis is correct before replacing any parts not visibly worn/broken. However Joe Customer who wants a 5 second diagnosis while the car was just driven 3 hours sometimes forces a guess on my part, those are usually the bad days of doing this job.

  36. Avataaar/Circle Created with python_avatars Dave Blane says:

    YOU are amazing!

  37. Avataaar/Circle Created with python_avatars hd the wise says:

    i forgot to tell you i pulled one wire no spark plugged back in grabbed a different one was leaning on the car and the spark jumped out of the good one the car kept
    running on one cylinder and i was screaming in firing order it was funny as all get-out dud dud dud ahhh went on for a time before i could get rid of the wire lol

  38. Avataaar/Circle Created with python_avatars Mike Chiodetti says:

    NICE PICO VIDEO. I need to practice more with mine now.

  39. Avataaar/Circle Created with python_avatars Medic Four says:

    Unfortunately I don't have a scope or know anyone who does…but I do have a complete parts car…so I have no choice but to play swapper if all the DVOM readings check out and I can't look at PRI/SEC waveforms for clues.
    Some year I might be able to afford an "old school" Vantage or VantagePro with my depressing medic paycheck. Sad that a people medic gets 9 bucks an hour and car medic gets 70.. :-0

  40. Avataaar/Circle Created with python_avatars Joe Lund says:

    Your the man

  41. Avataaar/Circle Created with python_avatars seftonplayer32 says:

    Love your process. Fix it right the first time. I hope to be as good as you with diagnosis work.

  42. Avataaar/Circle Created with python_avatars QQTrick1QQ says:

    PO300 should be illegal!

  43. Avataaar/Circle Created with python_avatars bsscards says:

    It may seem silly. Very true. I work at an Acura dealer, only one with a scope and everyone sees me as over-diagnosing cars, or trying to be better than the shop foreman. Irritating, I just wanna be a better tech.

  44. Avataaar/Circle Created with python_avatars Moving Up Auto Diagnostics says:

    Good diag bro, quick and easy.

  45. Avataaar/Circle Created with python_avatars jimmy threetoes says:

    Good scope work, always good to prove your suspicions.

  46. Avataaar/Circle Created with python_avatars Zvonimir Bobic ex- says:

    had you checked pwr n gnd while it was acting up, then it would ve been 100% verified 😉

  47. Avataaar/Circle Created with python_avatars Jeremiah Jorenby says:

    had a 2006 outback that would randomly misfire when hot, esp on restart, I cooled off the coil by pouring water on it and that fixed it, went to the dealer for the new part 3 days later and its been running fine since

  48. Avataaar/Circle Created with python_avatars bigtonkakid says:

    I hate when the windows have the Nico-tint!