Just bought this 07 Lexus 460 with 140,000 miles and getting horrible gas mileage ...does anybody know if they've had better gas mileage with a certain set of Spark plugs? Anything else I can do??? besides the K&N air filters, regular oil changes, fuel injector cleaner,....was going to have the fuel filter changed but it's in the tank so not going to worry about that.... thanks for the help!