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2018 M2 Competition Rough Idle & Misfires - P0301, P0302

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Nicole W. · rep 0 · May 22, 4:02 AM · 1 replies · solved · Question

Vehicle: 2018 BMW M2 Competition F87

Hey everyone,

My 2018 BMW M2 Competition (F87) with the S55 engine has developed a really rough idle lately. It feels like the engine is shaking more than usual, especially when cold. The Check Engine Light came on, and my scanner pulled P0301 and P0302 (Cylinder 1 and 2 Misfire Detected).

I've noticed a slight loss of power under acceleration, and sometimes it feels like it's struggling to rev smoothly. The car has about 38,000 miles on it. I'm running premium fuel, always have.

What should I be looking at first? Spark plugs? Ignition coils? Could it be something more serious like injectors? Any M2C owners experience similar issues?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:02 AM

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ClearTheCode admin answer:

Experiencing rough idle and misfires (P0301, P0302) on your 2018 BMW M2 Competition (F87) with the S55 engine points to a problem with the combustion process in cylinders 1 and 2. Given the mileage, several components could be at fault.

Here's a systematic approach to diagnose the issue:

  1. Spark Plugs: These are a common wear item. If the spark plugs in cylinders 1 and 2 are fouled, worn, or damaged, they won't provide a strong enough spark. It's recommended to replace all spark plugs at once, especially if they are due for service (typically every 30-60k miles depending on driving style and tune).
  2. Ignition Coils: A failing ignition coil for cylinder 1 or 2 would directly cause a misfire. You can try swapping the coils from cylinder 1 and 2 with coils from known good cylinders (e.g., 3 and 4) and see if the misfire codes follow the coils. If P0303 and P0304 appear, you've found your faulty coils.
  3. Fuel Injectors: Clogged or faulty fuel injectors for cylinders 1 and 2 could be delivering an incorrect fuel spray pattern or insufficient fuel, leading to misfires. This is less common than plugs/coils but a definite possibility, especially with direct injection engines. A fuel system cleaner might help if they are mildly clogged, but a faulty injector will need replacement.
  4. Compression Issues: While less likely for multiple specific cylinders without other symptoms, low compression in cylinders 1 and 2 due to valve issues or piston ring wear could cause misfires. A compression test or leak-down test would confirm this.
  5. Vacuum Leaks: Though typically causing lean codes (like P0171), a significant vacuum leak affecting specific cylinders could potentially contribute to misfires.

When to see a shop:

  • If swapping coils doesn't isolate the problem.
  • If you suspect fuel injector issues, as these require specialized tools for diagnosis and replacement.
  • If you notice any unusual noises from the engine or significant power loss.
  • A BMW specialist or dealership can perform advanced diagnostics, including injector flow tests, compression tests, and use BMW-specific software (ISTA) to pinpoint the exact cause of the misfires.
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