Is the Lexus LS 430 known to have motor problems
motor on 2003 Lexus LS430
There are no Technical Service Bulletins I see about common faults on that engine. Lexus did have a more recent recall on valve springs on certain engines not sure if this engine is affected. (3UZ-FE). Call your nearest Lexus dealer and ask them if there is any recalls on your car/engine.
Check out this page http://repairpal.com/lexus-ls430-2003/problems to find out problem reports.