we recently bought our rx300 and didnt know that we had to put high octane in it we use 92. we only used 2 tank full of regular unleaded knocking pretty bad, then we filled 3 times already with 92 octaine and still knocks but not as bad.... can anyone tell whats going on? dealer told me they replaced the knock sencor because the engine light was on before we bought it. engine miles about 125K and timing belt or chain in this engine V6

 

You should be able to drive the RX on 87 octane without knocking (that's what the knoock sensor system is for). If you just bought it take it back to the dealer. Was it a Lexus dealership? You have a timing belt on your engine with scheduled replacement at 90k but don't worry about it unduly at this point.

 

Is the engine light still on?

 

maybe the timing belt is off a notch?

 

Turn the key to the ACC position to be sure that the Check Engine light does light up - the dealer may have disconnected it, or it may have burnt out.