Tech notesThe P0300 code means that a cylinder(s) is misfiring or is randomly misfiring. Start by checking for intake leaks, intake gaskets are common caused of multi-cylinder misfiring. If no leak are found the next step is to replace the spark plugs. If the problem persists more tests needs to be done to diagnose problem, see "Possible Causes"
There is a factory service bulletin for the following KIA models:
The bulletin provides information on how to inspect and diagnose problems related to the Oil Control Valve (OCV) used in Constant Variable Valve Timing (CVVT), if at any time the OCV is suspected as the caused of rough idling, poor acceleration, camshaft timing misalignment-related trouble codes, misfire-related trouble codes.
Bulletin: Kia Constant Variable Valve Timing Oil Control Valve Inspection