Here are some of the useful information that I found while browsing the net.

The information is not for a Lexus, but the concept is the same.

C5Forum - LTFT - O2 Analysis & Tuning Guide
http://www.c5forum.com/diy/ltft.php

Modifying and Tuning your C5 Corvette
http://www.vetteguru.com/mods/howto/#air_fuel

C4 Mass Air Flow Sensor Facts - www.c4vettes.com
http://www.c4vettes.com/maf.htm
 

Engine Idle Control
http://www.autoshop101.com/forms/h26.pdf

Relative Horsepower Calculator
http://rshelq.home.sprynet.com/calc_hp_dp.htm

O2 ECU Coding
http://www.brownsword.ca/afmeters.html

[Club DSM] Oxygen (O2) Sensor
http://www.dsm.org/menu.epl?item=205