I've had this same problem the said it was the intake valve had it replaced and still doign the same thing now they say its something in the transmission. I just keep rolling the plugas and wires on this car last a looooooooong time and replacing the fuel pump/filter might help but really I can't get any true answere from lexus or any shop as to why this is happening......

Bad fuel pump. get it replaced. it is located in the fuel tank.