I had the same issue with
I had the same issue with the rough idle even after replacing spark plugs Exedra so I looked up the letter for the 9 year warranty unlimited mileage I contacted my local dealership and they are now replacing all the Pistons gaskets plugs excetera and it's all on Lexus is dying if you're having this issue I would suggest contacting your local dealership and having them honor the warranty for the carbon buildup