I have a 2009 Lexus IS250 with appox 133,000 miles. I have noticed that when I take long trips I get black soot on the chrome exhaust tips and light soot on the bumper molding surrounding the exhaust. I don't see any "smoke" when i start the engine or while in idle, nor do i have any warning messages or check engine indicator. Does this soot indicate a serious engine issue? I have been told that 133,000 miles really isn't considered high mileage for a Lexus. Any thoughts or advice would be appreciated. Thanks.