JSD, I had the same problem 3 years ago. All three lights would come on and eventually go off. The Lexus Dealer said it was the gas cap. The previous owners, a relative, did all the maint on the vehicle but Lexus still could not figure out why the lights came on. The one thing I noticed is my gas mileage suffered cause it was not running at optimum when they were on. Finally, I went to AutoZone and they read the codes for me. Oxygen sensors, up-stream, both of them. I checked around and most places wanted between $300.00 and $450.00 to do them both. If you are handy at all, you can spend $11.00 for the socket, or rent it from Auto Zone, and do it yourself. I ordered the sensors off the internet and saved about $100.00, put it up on ramps and in 45 minutes the lights were off and have yet to come back on. Vehicle has averaged out now at 19 mpg city.
I would say the only other thing I did was let it cool and spray some penetrating oil the night before to help loosen them.
That is my experience on those crazy three lights.