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Rough Idle and Misfire on my 2018 CX-5 - Check Engine Light Flashing!

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Dan C. · rep 0 · May 22, 4:47 AM · 1 replies · solved · Question

Vehicle: 2018 Mazda CX-5 Grand Touring

Hey everyone,

I've been having some trouble with my 2018 Mazda CX-5 Grand Touring lately. Over the past week, it's developed a really rough idle, especially when I'm stopped at a light. It feels like the engine is shaking more than it should.

Yesterday, the check engine light started flashing, and the car felt like it was losing power during acceleration. I pulled over and checked the codes with my OBD scanner, and it's showing P0301, indicating a misfire in cylinder 1.

Has anyone else experienced this with their CX-5? What was the fix? I'm hoping it's something simple like spark plugs, but I'm worried it could be something more serious. Any advice would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:47 AM

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ClearTheCode admin answer:

Experiencing a rough idle and a flashing check engine light, especially with a P0301 code, points directly to an engine misfire. Here's a breakdown of common causes and what to do:

  1. Identify the Misfire Cause:

    • Spark Plugs: Worn or fouled spark plugs are a very common cause of misfires. If cylinder 1's plug is old or damaged, it won't ignite the fuel-air mixture properly.
    • Ignition Coils: A failing ignition coil for cylinder 1 would prevent the spark plug from firing correctly. This is also a frequent culprit.
    • Fuel Injector: A clogged or faulty fuel injector for cylinder 1 could be delivering too little or too much fuel, leading to an improper mixture.
    • Vacuum Leaks: Leaks in the intake manifold or vacuum lines can cause unmetered air to enter the engine, leading to a lean condition and misfires, though usually this would affect multiple cylinders or cause a P0171/P0174 code.
    • Compression Issues: Less common, but low compression in cylinder 1 due to valve issues or piston ring wear can cause a misfire.

  2. Initial Troubleshooting Steps:

    • Check Spark Plug: If you're comfortable, inspect the spark plug for cylinder 1. Look for signs of wear, oil fouling, or damage.
    • Swap Coil Pack: A common diagnostic trick is to swap the ignition coil from cylinder 1 with a coil from another cylinder (e.g., cylinder 2). If the misfire code then moves to cylinder 2 (P0302), you've identified a bad coil pack.

  3. When to See a Shop:

    • Immediately: A flashing check engine light indicates a severe misfire that could be damaging your catalytic converter. Driving with a persistent flashing light is not recommended.
    • If Swapping Coils Doesn't Help: If the misfire remains on cylinder 1 after swapping coils, or if you're not comfortable performing these checks yourself, it's time to take your CX-5 to a qualified mechanic. They can perform more in-depth diagnostics, including fuel pressure tests, injector tests, and compression tests, to pinpoint the exact issue and prevent further damage.
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