There was quite a bit of discussion on this broad subject a while back when I last visited this forum and I elicited several suggestions regarding my check engine light and related trouble code, ranging from ordering new O2 sensors on the Internet to putting a fuel additive in my gas. I decided to just ignore the light since I was experiencing no discernible "symptoms," until it was time for my annual state mandated emissions test. I then discovered my state MVD would not even test the vehicle if a check engine light was activated, which mine was. After considering all the forum suggestions again, I decided to take my '99 300 to the local Lexus dealer/service center for their own diagnosis and was told a specific sensor needed to be replaced for almost $400 parts & labor. I recalled one forum suggestion had been to simply clean the sensor, so I asked the service manager to try that instead of replacing it. He only reluctantly agreed, telling me he could not warrant the procedure or certify a repair for purposes of MVD requirements. Well, the cleaning took only a few minutes and they charged me $88 for it. My car passed the emissions test and now, several months later, the light has still not returned so far.
Thought it was worth passing this on.