I was having major problems with pinging on my 2001 rx300 right after I bought it (51,000 miles). Did numerous decarbs (by the dealer), checked everything possible, always ran premium gas, fought with lexus customer satisfaction and lost. Bit the bullet and had them replace the knock sensors (both of them). $900 - $1,000, but it actually worked. It's a shame they wouldn't cover it, but I'm glad it's fixed.