I had same problem with my 99 RX300. Did research on what can I do to fix it with minimum $$$ contribution as I didn't want to spend $160-$130 for damn sensor( I am not talking about going to dealership and spend $$$$$ for no reason) What I found is Denso O2 sensor, not air flow sensor everybody talking about. My original AF sensor was 89467-48011 and I installed Denso 234-9009 O2 instead of it for $50 only, on
ebay!!!!! Reset check engine light, disconnect battery, take the old one out and put the new on in, connect the battery, Done. Drive 50-60 miles and go to emmission test. Hope this information will help someone.