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2018 Mini Cooper S - P0301 Misfire and rough idle after cold start

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Heather Y. · rep 0 · May 22, 6:51 AM · 1 replies · solved · Question

Vehicle: 2018 Mini Cooper S

Hey everyone,

My 2018 Mini Cooper S, with about 65,000 miles, has recently started acting up. This morning, after a cold start, the engine was running really rough, and the Check Engine Light came on. It felt like it was struggling to maintain idle, and there was a noticeable vibration.

I managed to get it to AutoZone to pull the codes, and it came back with a P0301 - Cylinder 1 Misfire Detected. It seems to run a bit better once it warms up, but the CEL stays on, and I can still feel a slight hesitation when accelerating.

Has anyone experienced this with their F56 Cooper S? What should I be looking at first? I'm hoping it's something relatively simple and not a major engine issue. Any advice on troubleshooting steps would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 6:51 AM

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ClearTheCode admin answer:

The P0301 code indicates a misfire specifically in cylinder 1 of your 2018 Mini Cooper S. This is a common diagnostic code and can stem from several issues. Addressing it promptly is important to prevent further engine damage.

Here are the common causes and troubleshooting steps:

  1. Spark Plugs: Worn or fouled spark plugs are a very common cause of misfires. Given your mileage, it's a good time to inspect and potentially replace all spark plugs, not just the one in cylinder 1. Mini recommends spark plug replacement around 60,000 miles for many models.
  2. Ignition Coils: A failing ignition coil for cylinder 1 would directly cause a misfire. You can often diagnose this by swapping the coil from cylinder 1 with a coil from another cylinder (e.g., cylinder 2). If the misfire code then changes to P0302, you've identified a faulty coil.
  3. Fuel Injector: A clogged or faulty fuel injector for cylinder 1 can prevent proper fuel delivery, leading to a misfire. This can be tested by a mechanic using specialized equipment or by swapping injectors (though this is more involved than swapping coils).
  4. Compression Issues: Less common but more serious, low compression in cylinder 1 due to worn piston rings, a faulty valve, or a head gasket issue can cause a misfire. A compression test or leak-down test would be necessary to diagnose this.
  5. Vacuum Leaks: While less likely to cause a single-cylinder misfire, a significant vacuum leak could affect engine performance and potentially contribute to misfires.

When to See a Shop:

If you've checked the spark plugs and swapped ignition coils without resolving the issue, or if you're uncomfortable performing these diagnostics yourself, it's best to take your Mini to a qualified mechanic. They have the tools and expertise to perform more advanced diagnostics, such as fuel pressure tests, injector flow tests, and compression tests, to accurately pinpoint the root cause of the P0301 code and ensure your engine is running optimally.

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