Could be a the temp sensor or a dirty ISC valve.
Lookup NC's posts. In one of them, if I can recall correctly, he mentions something about off throttle shock creating reverse torque. I didn't bookmark the post, but I did download the Toyota TSB for this. You'll find it here:
http://us.lexusownersclub.com/forums/index...ost&id=8682
Thanks for the info I think I'll replace the temp sensor. But, I guess there are two temp sensors. One I think is a temp sendor and the other is the temp sensor not to sure which one tells the ECU when it's warm or cold. I think it's the temp sender. not sure.