Engine misfire
A misfire means one or more cylinders are not burning the air-fuel mix on schedule.
Drivers often feel a stumble, a shaking idle, or a flashing check-engine light under load. The ECU stores a random misfire as P0300 and a single cylinder as P0301 and the codes that follow it.
Typical checks start with spark, coil, plug, injector, and vacuum leaks before any part is replaced. Read the stored code and freeze frame, then open the matching DTC page.
A trouble code marks a condition to test. It does not by itself prove which part to replace.