2020 Hyundai Tucson - P0300 Random Misfire / Low Power

Question

My 2020 Tucson (just out of warranty) is throwing random misfire codes. It feels very sluggish, especially when trying to merge onto the highway. If I'm cruising at 60mph and need to speed up, the car jerks and hesitates significantly.

I've replaced the spark plugs with the factory-spec NGK Iridiums, but it didn't change anything. The coils seem fine when I test them. One thing I noticed is that the intake values look a bit oily. Could this be a fuel injection issue or something internal?

ShopBossMike · Answer

✅ Confirmed fix: This is a classic GDI (Gasoline Direct Injection) issue. Since fuel doesn't spray over the intake valves, carbon builds up until it restricts airflow and causes turbulence, leading to misfires.

I performed a manual walnut blasting of the intake valves to remove the 'coking.' The valves were heavily coated in black carbon. After cleaning the valves and performing a GDI fuel system service to clean the injectors, the power returned and the misfires are gone. I recommend an oil catch can to prevent this from returning so quickly.

OTR_Carlos · Answer

You might have a failing High-Pressure Fuel Pump (HPFP). These are driven by the camshaft and can leak fuel internally into the oil, or just fail to provide sufficient pressure to the rail under load. Check your dipstick for the smell of gasoline; if it smells like a gas station, that HPFP is toast.

2020 Hyundai Tucson - P0300 Random Misfire / Low Power

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