I just replaced the knock sensors in my 99. The car was driving okay, but periodically the RPMS would climb. The knock sensor causes the tranny to not go into OD. THe knock sensors are located underneath the intake manifold, and cost about 160 to 180 each. You must also replace about 3 gaskets. I also had the Harness replaced because heat had made it brittle, and the ends snapped just from being touched. New harness was 35 dollars. 600 to 700 dollars to replace the above mentioned items at my independent lexus mechanic shop.