Thanks jaswood - already replaced the all 6 spark plugs and the coil of the cylinder that's been misfiring. Still no go. Then the mechanic went to do compression test on the engine and made the "head rebuild" recommendation. I'll ask about the fuel injector but my guess is that the culprit isn't there. Thanks again! I would first replace the fuel injector, spark plug, and ignition coil just for that cylinder as an inexpensive "trial".
Fellow Rx300 owners: Trouble alert - it started as a check engine light with cylinder #2 misfiring on my 2002 Rx300. Took it to a mechanic that I have been using and he told me that the piston seal is burnt and the top half of the engine needs to be taken out to get rebuilt. The cost is US$2k. It was believed that the culprit was that I have been using octane 87 gas instead of 91. I have a little over 110k miles on my '02 Rx300 Do you folks have any experience on the need to rebuild? Do you always use octane 91 gasoline? Does it sound like a reasonable job? Best regards, Vic