What causes P0300 on a Kia Forte?

Common causes of P0300 on Kia Forte: Ignition coil failure on 2.5L Smartstream or 1.6L turbo (Elantra/Sonata/Forte/K5); Spark plug fouling from oil consumption due to Theta II engine bearing failure (recalled models); Carbon buildup on intake valves from GDI on 2.0L and 2.4L Theta II engines; Low fuel pressure from high-pressure fuel pump (HPFP) degradation on GDI engines; CVVT (variable valve timing) solenoid failure causing erratic cam timing.

P0300

P0300 Kia Forte

Q: How much does it cost to fix P0300 on a Kia Forte?

Fixes for P0300 on Kia Forte include: Replace all ignition coils and spark plugs with Hyundai/Kia OE Denso or NGK parts, Check engine for rod bearing knock recall eligibility; replace engine if affected by recall, Perform walnut shell blasting on intake valves on GDI-only engines, Replace high-pressure fuel pump and verify rail pressure meets specification, Replace CVVT oil control valve (solenoid) and inspect for oil sludge buildup.

Random/Multiple Cylinder Misfire Detected · Powertrain Code · High · Repair: Moderate

What is P0300?

The ECM has detected misfires occurring in multiple or random cylinders. Common causes include worn spark plugs, faulty ignition coils, vacuum leaks, low fuel pressure, or a failing catalytic converter.

When the Kia Forte triggers code P0300 (random/multiple cylinder misfire detected), it typically points to an issue in the powertrain system. This is a high severity code, so address it promptly to avoid further damage or safety concerns. Below you'll find the most common causes, symptoms, and repair options specific to the Kia Forte.

This repair is rated moderate, meaning some experience and specialty tools required.

Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Kia Forte.

Common Causes on Kia Forte

Ignition coil failure on 2.5L Smartstream or 1.6L turbo (Elantra/Sonata/Forte/K5)
Spark plug fouling from oil consumption due to Theta II engine bearing failure (recalled models)
Carbon buildup on intake valves from GDI on 2.0L and 2.4L Theta II engines
Low fuel pressure from high-pressure fuel pump (HPFP) degradation on GDI engines
CVVT (variable valve timing) solenoid failure causing erratic cam timing

Symptoms

Rough idle with noticeable engine vibration
Engine shaking or stumbling under load
Loss of power during acceleration
Check engine light flashing intermittently
Poor fuel economy
Hesitation or stumble on acceleration

Recommended Fixes

Replace all ignition coils and spark plugs with Hyundai/Kia OE Denso or NGK parts

Check engine for rod bearing knock recall eligibility; replace engine if affected by recall

Perform walnut shell blasting on intake valves on GDI-only engines

Replace high-pressure fuel pump and verify rail pressure meets specification

Replace CVVT oil control valve (solenoid) and inspect for oil sludge buildup

Notes for Kia Forte

Check NHTSA recall 20V-750 for Theta II engine bearing failure before extensive misfire diagnosis.

P0300 Kia Forte

What is P0300?

Common Causes on Kia Forte

Symptoms

Notes for Kia Forte

Check Kia Forte Specs