Had this problem with mine not long after buying it. Car was out of warranty and had done about 64,000 miles. Had AA come out to it and the fault was read as a problem with the EGR. Car went to Lexus Nottingham and even though it was out of warranty Lexus fixed it which consisted of the engine being rebuilt including new pistons, new EGR, cat and supplied with a courtsey car for 3 weeks while it was done and all done for no cost to myself.The car was not bought form a Lexus dealer so all in a good result.
Car has now done 95,000 miles and still seems ok but do take it for a regular run at high revs to try and keep it clean.