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My engine on my 2014 Corolla started to sputter and I took it to a mechanic who replaced the #2 ignition coil and all the spark plugs. A week later the engine started to act up again, but only after it had been running for a while 15-20 minutes on hot summer days. If I left it for a few hours it would run fine again initially for another 15-20 minutes. I had the coil replaced again but the problem started to re-occur a few days later.

OBD shows cylinder 2 misfire (and at some point also showed an air/fuel ratio mismatch, I assume from unburnt fuel from the misfire).

What could be the possible issue and what can I do to diagnose the problem myself?

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  • Welcome to Motor Vehicle Maintenance & Repair! I'm wondering if there's a grounding problem. I wouldn't know how to test it, but you could just try removing the coil and reinstalling it straight away to see if the problem temporarily goes away. Just thinking outloud. Jul 26 at 23:57
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    @Pᴀᴜʟsᴛᴇʀ2 add a wire from the coil fixing point to a known good ground point...
    – Solar Mike
    Jul 27 at 5:53
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    Swap the coil on cylinder 2 with one of the other coils and see if the fault stays with cylinder 2. Maybe you have a bad connector on bad harness, or a bad ECU or ignition amplifier if there is one.
    – HandyHowie
    Jul 27 at 6:19
  • @SolarMike - Good point. Just disconnecting and reconnecting from the wiring harness would also prove what I was wondering. Jul 27 at 22:08
  • Hmm, I'm pretty sure I can already rule out the ignition coil itself, given that it has been replaced twice already. As for grounding, it's strange that a grounding problem would occur only after running for some time, but I'll try it.
    – bitporter
    Jul 28 at 21:13

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