I bought this car 6 months before when it had only 50000 miles on it. It ran for 6 months with out any problems since I owned it. I used to do the required maintenance regularly. When it got around 75000 miles on a cold day the check engine and VSC lights turned on. When I took to the dealer they said, knock sensors had gone bad and need replacement.
Gave an estimate of about $800.00 to replace both sensors. I said I would get back to them within couple of days.
Surprisingly the lights went off next day and I learned the lights may even turn on when the fuel tank is not closed tightly. But that did not last long. The lights came again after a day and thereafter I did not worry much thinking the lights would go off eventually. I also experienced some power loss when I applied gas and the vehicle could not accelerate enough.
Hoping the Knock would have been caused by bad gas, I asked the dealer about it. The dealer told me generally 87 would be good for Lexus RX300. But even I was using 89 to be in the safer side the lights did not go.
I am now spending $1000.00 along with some other issues to replace the sensors. But I am not sure whether it will permanently solve the issue or not.
Later I learnt that RX300 model is definitely not a maintenance free vehicle since this is one of the design issues the model has.