If your 12 volt battery has ever been run below 7 volts or been disconnected (I forgot to ask if you've ever disconnected it) or replaced you may need to do the ISC learning procedure. You may want to do this anyway just for peace of mind. If you're not comfortable doing it yourself, the dealer can hook it up to their computer but it will cost you.
As per the Lexus TSB -
"It is important to perform the ISC Learning procedure anytime the 12–volt battery is
disconnected or the voltage falls below 7 volts. This procedure allows the I.C. (internal
combustion) Engine to re–learn its optimal idle speed during the initial engine warm–up
cycle or charging the HV battery. If this procedure is NOT performed, the following
customer complaints may occur:
Engine runs too long or more frequently than normal
Reduced fuel economy
Transmission gear “clatter” noise at idle is more pronounced"
Many who have done this procedure have experienced increased gas mileage (myself included).
Check here -
http://us.lexusownersclub.com/forums...30&hl=learning