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2018 CX-5 Rough Idle and Misfire Code P0301

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Ashley M. · rep 0 · May 22, 4:49 AM · 1 replies · solved · Question

Vehicle: 2018 Mazda CX-5 Grand Touring

My 2018 Mazda CX-5 Grand Touring, with the 2.5L engine, has been idling really rough lately. It's most noticeable when I'm stopped at a light or in slow traffic.

The check engine light came on a couple of days ago. When I scanned it with my OBD-II reader, I got a P0301 code, indicating a misfire on cylinder 1. The car feels a bit sluggish too, especially during acceleration from a stop.

I'm wondering what the common causes for this issue are on these models. Could it be something simple like a spark plug, or something more serious? Any advice on where to start troubleshooting would be greatly appreciated.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:49 AM

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ClearTheCode admin answer:

A P0301 code specifically points to a misfire in cylinder 1. This is a common issue with several potential causes, and troubleshooting usually involves a systematic approach.

  1. Check Spark Plugs and Ignition Coils: The most common culprits for a misfire are a faulty spark plug or a failing ignition coil for that specific cylinder. Start by inspecting the spark plug in cylinder 1 for wear, fouling, or damage. If it looks bad, replace it. You can also swap the ignition coil from cylinder 1 with another cylinder (e.g., cylinder 2) and see if the misfire code moves to the new cylinder (e.g., P0302). If it does, the coil is bad.
  2. Inspect Fuel Injector: A clogged or faulty fuel injector for cylinder 1 can also cause a misfire. You can test the injector's resistance or have a shop perform a fuel pressure balance test to see if it's delivering the correct amount of fuel.
  3. Vacuum Leaks: Less common for a single-cylinder misfire but still possible, a vacuum leak near cylinder 1 could lean out the air-fuel mixture, causing a misfire. Listen for hissing sounds or use a smoke machine to detect leaks.
  4. Compression Test: If the above steps don't resolve the issue, a compression test on cylinder 1 is crucial. Low compression indicates an internal engine problem, such as worn piston rings, a faulty valve, or a blown head gasket, which would require more extensive repair.

When to See a Shop:

If you've checked the spark plug and ignition coil and the problem persists, or if you're uncomfortable performing these diagnostics yourself, it's best to take your CX-5 to a qualified mechanic. They have specialized tools to accurately diagnose fuel system issues, perform compression tests, and identify more complex internal engine problems. Continued driving with a persistent misfire can lead to catalytic converter damage, which is a very expensive repair.

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