Genesis G90 II: Flickering Check Engine Light and Rough Idle

What a Flickering Light Usually Means

A steady check engine light says the ECU has stored a fault; a flickering one often means an active misfire is happening right now. On the Genesis G90 II, that can feel like a rough, shaky idle that comes and goes. The engine may be dropping a cylinder intermittently because of weak ignition, a lean air-fuel mixture, or a sensor signal the computer cannot trust. Do not ignore it: unburned fuel can overheat the catalytic converter.

Check These Parts and Sensors First

• Spark plugs and ignition coils: Worn plugs, a failing coil, or a cracked coil boot are common causes of an intermittent misfire and rough idle.
• Vacuum and intake leaks: A split intake hose, leaking valve cover gasket, or loose PCV connection can lean out the mixture and make the idle stumble.
• Mass airflow and throttle body: A dirty or failing MAF sensor and carbon buildup on the throttle body can upset idle control, especially when the fault comes and goes.
• Fuel delivery: Weak fuel pressure, a clogged injector, or a tired high-pressure fuel pump can cause lean misfires and uneven idle.
• Camshaft and crankshaft position sensors: Intermittent signals can confuse timing and spark delivery, so check for related codes and live data.

Start with a full scan that reads manufacturer-specific codes, misfire counters, fuel trims, and freeze-frame data. A mechanic can swap coils or run a compression and leak-down test if the misfire is not obvious.

Is It Safe to Keep Driving?

If the light is flickering or flashing, treat it as a stop-driving warning, especially if it happens under acceleration. You can often drive gently to a nearby shop if the light is steady and the car is not overheating or shaking violently, but with a rough idle and flicker, I would limit driving to a short trip to a qualified Genesis technician. Continuing to drive can turn a spark plug or coil job into a costly catalytic converter repair.

This material is AI-generated and for informational purposes only — it does not replace an in-person diagnosis by a qualified mechanic.