The 2022 MINI Cooper triggering P0300 with rough idle indicates random misfires across multiple cylinders. This turbocharged three-cylinder or four-cylinder engine (depending on variant) requires systematic diagnosis to identify the root cause.
Cooper Engine Options
The 2022 MINI Cooper offers both three-cylinder (B38) and four-cylinder (B48) turbocharged engines. Identify your engine configuration—the three-cylinder has unique characteristics while the four-cylinder shares architecture with BMW vehicles.
Random Misfire Characteristics
P0300 indicates misfires across multiple cylinders without a consistent pattern. This typically points to system-wide issues—fuel quality, vacuum leaks, or ignition power problems—rather than single component failure. The rough idle results from unpredictable combustion irregularity.
Ignition System Testing
Despite random misfires, ignition components remain primary suspects. Inspect all ignition coils for damage, cracks, or carbon tracking. Check spark plug condition—the turbocharged engines are demanding on plugs. Replace plugs per MINI's interval recommendations.
Vacuum and Boost Leaks
Turbocharged MINIs have numerous pressurized connections that can develop leaks. Boost leaks cause lean conditions triggering misfires. Smoke testing the intake and boost system effectively reveals leaks invisible to visual inspection.
Direct Injection Carbon Buildup
MINI's direct injection engines deposit carbon on intake valves since fuel doesn't wash valve faces. Carbon accumulation reduces valve sealing and causes misfires. This affects multiple cylinders similarly, consistent with random misfire patterns.
Fuel Quality
Premium fuel is required for turbocharged MINIs. Lower octane causes knock that may appear as misfires. Contaminated fuel affects all cylinders equally.
Repair Costs
Ignition coil replacement costs $150-300 per coil at MINI dealers. Spark plug service runs $200-400. Carbon cleaning for direct injection engines ranges $500-1,000. Boost hose replacement costs $150-350.