Misfire and short hesitant idle during start up

Discussion in 'Mazdaspeed 3 Troubleshooting' started by eels, May 11, 2022.

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  1. eels

    eels Greenie N00B Member

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    Location:
    Meridian, ID
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    Just bought my first speed about two weeks ago so Im sorry if I come off noobish in this post
    Year/Make/Model: 2008 Mazdaspeed 3
    Mileage: 123000
    Location/Alitutude: Meridian, ID (2,605' sea level)
    Concern: Misfire on cyl 3. Weird idle during startup. Overheats and burning electrical smell (might be unrelated)
    DTC's: P0303
    Modifications: Completely stock to my knowledge.
    ECU/Tuning Software: Cobb Accessport V3
    Tuner: No tune
    Is the concern intermittent? No... Always has the same weird idle.
    Recent Repairs: Oil change. NGK Iridium IX TR7IX spark plugs gapped to .28

    The first minute during startup starts with a high and inconsistent/ hesitant sounding idle and eventually smoothes out to normal within a minute. Also, I don't know if this is a separate or related issue, but the engine appears to overheat despite the coolant temp always remaining within operating temp (under 215 F) Even when driving for 30 plus minutes the radiator fan never turns on and I can notice a burning electrical smell around 15 minutes of driving. The engine feels way too hot when I pop the hood after a drive. No codes besides the P0303.

    I changed the spark plugs and oil right when the misfire code happened and realized the previous owner had them gapped at .35 (ouch) but it did not resolve the CEL or the weird idle. After the idle smoothes out I don't notice anything different about the driving (still pulls real nicely) other than it can be a little jerky when decelerating in a low gear and the overheating issue. I switched the 2nd and 3rd coil packs but the misfire still occurred on the 3rd cyl.
    I haven't compression tested or inspected the fuel injectors yet. VVT was done 20,000 miles ago.

    Can anyone give me some guidance on what I should do next?
     
  2. Easter Bunny

    Easter Bunny Professional Engineer Motorhead Platinum Member

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    Does your battery have a good charge? A weak battery can cause all kinds of weird idle issues

    Check for vacuum leaks
     
    Easter Bunny, via a mobile device, May 11, 2022
    #2
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