A rough idle or cylinder misfire can reflect ignition, fuel delivery, air leaks or mechanical condition. The IS 250 and IS 350 have different engine configurations and diagnostic considerations.
How the concern should be evaluated
Use cylinder-specific fault data, ignition and fuel checks and appropriate mechanical testing rather than assuming all rough-running complaints are carbon buildup.
When to contact a Lexus repair shop
If you notice an abnormal sound, warning light, fluid leak or drivability change, call Mich’s Foreign Cars with the year, exact model, powertrain, symptom history and any previous repairs. Service availability depends on the system and required equipment.