This bulletin applies to 2008 Lexus LS600H vehicles with the MIL on and DTC P030# stored after a spark plug change. In most cases P0300 is stored. The vehicle may run rough and misfire on cold starts and under acceleration.
The installation of conventional spark plugs in engines that require “long reach” type spark plugs can contribute to this condition. Verify that the correct “long reach” spark plugs are installed.