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2018 Cooper S Misfire and Rough Idle - P030X codes

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Chris P. · rep 0 · May 22, 6:54 AM · 1 replies · solved · Question

Vehicle: 2018 Mini Cooper S

Hey everyone, I'm having some trouble with my 2018 Mini Cooper S. Lately, it's developed a really rough idle, especially when cold, and I've noticed a significant loss of power under acceleration. The check engine light came on, and when I scanned it, I got P0301, P0302, and P0300 codes, indicating misfires on cylinders 1 and 2, and a random/multiple misfire.

I've read that carbon buildup can be an issue with these direct-injection engines, but I'm not sure if that's what I'm dealing with. Could it be spark plugs, ignition coils, or something more serious like the high-pressure fuel pump?

Any advice on where to start troubleshooting would be greatly appreciated. Thanks!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 6:54 AM

0

Hello Chris,

Misfires in direct-injection engines like those found in your 2018 Mini Cooper S are a common concern, and the P0300, P0301, and P0302 codes confirm that your engine is experiencing issues with combustion. Here's a breakdown of potential causes and diagnostic steps:

  1. Common Causes for Misfires:

    • Spark Plugs: Worn or fouled spark plugs are a frequent culprit. They should be replaced according to your Mini's maintenance schedule, typically every 30,000-60,000 miles. Carbon buildup on the electrodes can also cause issues.
    • Ignition Coils: A failing ignition coil can prevent a spark plug from firing correctly. Since you have misfires on specific cylinders (1 and 2), it's possible one or both of these coils are faulty.
    • Carbon Buildup: Direct injection engines are prone to carbon deposits on the intake valves because fuel is injected directly into the cylinder, bypassing the valves. This buildup can restrict airflow and cause misfires, especially at idle.
    • Fuel System Issues: This could include clogged fuel injectors, a failing high-pressure fuel pump (HPFP), or a low-pressure fuel pump issue. A weak fuel supply to specific cylinders can lead to misfires.
    • Vacuum Leaks: Unmetered air entering the engine can lean out the air-fuel mixture, leading to misfires.

  2. Diagnostic Steps You Can Take:

    • Inspect Spark Plugs: Remove and visually inspect the spark plugs from cylinders 1 and 2. Look for signs of wear, fouling, or damage. Consider replacing them if they are due or look suspicious.
    • Swap Ignition Coils: To determine if an ignition coil is at fault, swap the coils from cylinders 1 and 2 with coils from known good cylinders (e.g., 3 and 4). Clear the codes and drive the car. If the misfire codes move to cylinders 3 and 4, you've identified faulty coils.
    • Check for Vacuum Leaks: Listen for hissing sounds around the intake manifold and vacuum lines. A smoke test can definitively identify leaks.
    • Fuel Pressure Test: This requires specialized tools but can help diagnose HPFP or low-pressure fuel pump issues. Low pressure would indicate a problem with the fuel delivery system.

  3. When to See a Shop:

    • If basic diagnostics (spark plugs, coils) don't resolve the issue.
    • If you suspect carbon buildup, as this requires a specialized cleaning procedure (walnut blasting).
    • If fuel system components like the HPFP or injectors are suspected, as these require proper diagnostic equipment and expertise.
    • If the misfire is severe, driving the car can damage the catalytic converter due to unburnt fuel entering the exhaust. It's best to have it towed if the misfire is constant and severe.
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