The smooth, refined idle of your 2022 Lexus RX has given way to an unsettling roughness, and a scan reveals P0300—Random/Multiple Cylinder Misfire Detected. Unlike cylinder-specific codes, P0300 indicates combustion problems affecting multiple cylinders, pointing toward a system-wide issue rather than a single failed component.
Understanding P0300 on the RX
The 2022 RX may have the naturally-aspirated 3.5L V6 (RX 350) or the hybrid powertrain (RX 450h). Either way, P0300 indicates the engine computer detected misfires occurring across multiple cylinders without a consistent pattern. This actually helps diagnostically—it suggests investigating shared systems rather than individual components.
Common Causes of Random Misfires
The V6 in your RX can develop random misfires from:
- Fuel quality issues - Contaminated or low-octane fuel affects all cylinders
- Ignition coil degradation - Multiple coils weakening simultaneously
- Spark plug wear - All plugs installed together age at similar rates
- Vacuum leaks - Unmetered air creates lean conditions across cylinders
- Mass airflow sensor problems - Incorrect readings affect fuel delivery
- Fuel delivery issues - Weak fuel pump or clogged filter
- Carbon buildup - Deposits on intake valves (if direct injection)
Lexus Reliability Context
Lexus vehicles typically demonstrate exceptional reliability, so random misfires on a 2022 model warrant thorough investigation. Consider recent changes—different fuel station, recent service work, or even a software update that might need recalibration.
Diagnostic Approach
For P0300, focus on shared systems:
- Check freeze frame data for conditions when misfires occurred
- Monitor individual cylinder misfire counts—even with P0300, some may be worse
- Test for vacuum leaks using smoke testing
- Verify fuel pressure at idle and under load
- Inspect spark plugs for consistent wear patterns
- Check for any recent recalls or TSBs
Repair Costs for 2022 RX
- Spark plug replacement (V6): $250-$450
- Ignition coil set: $400-$700
- Vacuum leak repair: $150-$400
- MAF sensor: $200-$350
- Fuel system cleaning: $150-$300