Ignition coil-on-plug failure / misfire

Symptoms

Rough idle, jerking at ~100 km/h, flashing CEL, poor fuel average

Likely cause

Coils age with heat; cheap non-OEM coils re-fail; oil in plug tubes from a leaking valve-cover / tube seal; broken IGF wire

Fix

Swap coils to confirm; fit OEM/Denso coils; replace plugs; fix tube-seal oil leaks; check the IGF circuit

Applies to

All petrol E120

Related fault codes

P0300-P0304, P0351-P0354 (newer ECUs); RM821E: P1300/P1305/P1310/P1315 igniter circuit

Confidence

medium

Sources

• pakwheels.com/forums/t/corolla-2004-se-saloon-1-6-at-bad-fuel-average-
• pakwheels.com/forums/t/corolla-altis-ignition-coils/1923155?page=2
• technician.academy/toyota-coil-on-plug-diagnosis-matthew-shanahan/
• toyotanation.com/threads/corolla-going-through-coil-packs.1732073/
• toyotamanuals.gitlab.io/RM01J1E/htmlweb/rm01j1e/rm/rm821e/m_05_0081.pd

Related problems on this car

• Upstream O2 sensor ageing
• Intake manifold gasket vacuum leak (1ZZ)
• Poor fuel average after a bad tune-up
• Dirty MAF sensor

Similar problems on other cars

• Misfire from coil / carbon · Toyota Passo (1st gen)
• Blocked catalytic converter · Toyota Passo (1st gen)
• A/C load: idle vibration & poor pick-up with A/C on · Toyota Passo (1st gen)

Where the parts are · Warning lights · Fault codes · Maintenance

Guidance only – confirm with a mechanic before repairs. All common problems