Knock Sensors

[chelo]

Hello...i recently purchased a 2000 lexus rx300 with 84,000 km(not miles). Car was running great when i test drove it. However, after 4 days, the engine light came on. Immediately i noticed that the car lagged behind and would rev much higher to move than it did before. I got it checked out, and it ends up that the knock sensor was down. The certified Lexus mechanic told me to disconnect the battery for 2 seconds and see if the engine light turns off, and it did! The car was running back to normal.( no lagging or high reving)

However, the day after the light came back on. Immediately i took the car back to the mechanic and he changed one of the knock sensors for about $500.00. Car ran great for two days and then engine light came back on. Got it checked and shows the knock sensor again.

I don't know what to do now. Has anyone experienced this before and have any suggestions, please help!

I'm also only getting about 390 km on a full tank because it is reving high.

Thanking you in advance to anyone who can help. Writing to you fro Canada..eh!