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2018 Mini Cooper S Rough Idle and P0302 Misfire

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Mike T. · rep 0 · May 24, 4:00 PM · 1 replies · solved · Question

Vehicle: 2018 Mini Cooper S

Hey everyone, I've got a frustrating issue with my 2018 Mini Cooper S (F56). Lately, it's developed a really rough idle, especially when starting cold. The engine feels like it's shaking more than usual, and I've noticed a definite loss of power and some hesitation under acceleration.

The check engine light came on last week, and it's been pretty consistent since. I scanned it with my OBD-II reader, and it pulled a P0302 code, indicating a misfire in cylinder 2. Sometimes it feels like the whole car shudders.

I'm hoping it's something relatively simple like a spark plug or an ignition coil, but I'm worried it could be something more serious. Has anyone experienced this with their F56 Cooper S? Any advice on where to start troubleshooting would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 24, 4:00 PM

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ClearTheCode admin answer:

It sounds like you're dealing with a classic misfire scenario, and the P0302 code specifically points to cylinder 2. Addressing this promptly is important to prevent potential damage to your catalytic converter.

Here are the common causes and diagnostic steps for a P0302 misfire on your 2018 Mini Cooper S:

  1. Faulty Spark Plug: A worn, fouled, or damaged spark plug in cylinder 2 is a very common culprit. They are relatively easy to inspect and replace.
  2. Defective Ignition Coil: The ignition coil for cylinder 2 might be failing, leading to an inconsistent or absent spark. This is also a frequent cause of misfires.
  3. Clogged or Failing Fuel Injector: If the fuel injector for cylinder 2 isn't delivering the correct amount of fuel, it can cause a lean or rich misfire. This is less common than spark/coil issues but definitely possible.
  4. Vacuum Leak: A localized vacuum leak near cylinder 2 could be leaning out the air-fuel mixture, causing a misfire. Inspect intake manifold gaskets and vacuum lines.
  5. Carbon Buildup: Direct injection engines like those in the F56 Mini are prone to carbon buildup on the intake valves. Severe buildup can impede airflow and cause misfires.
  6. Low Compression: In more severe cases, an internal engine issue like a worn piston ring or a faulty valve in cylinder 2 could lead to low compression and a misfire.

When to See a Shop:

  • If swapping spark plugs and ignition coils doesn't resolve the issue, or if the misfire moves to a different cylinder after a swap, you've likely identified the faulty component.
  • If you suspect a fuel injector issue, significant carbon buildup, or low compression, it's best to consult a qualified Mini specialist. They have the diagnostic tools and expertise to perform fuel pressure tests, compression tests, and potentially scope the intake valves for carbon buildup.
  • Continued driving with a persistent misfire can lead to unburnt fuel entering and damaging your catalytic converter, which is a very expensive repair. Get it checked out soon!
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