Hi,

Just need a little help,I'm about to take install knock sensors in my 98 Lexus es300, is there a special torque(ft,lbs measurement) I'm suppose to tighten them too...please let me know

 

29 ft-lb

Also make sure you buy Denso brand knock sensors only. I can not stress this enough, do not buy any other brand other than Denso for your knock sesnors.
While you are doing this job you may want to consider your coolant bypass hose, knock sensor connector, intake gaskets, rear spark plugs / ignition coils and fuel injectors.

 

^this. Also stay away from the "Denso" sensors on eBay that are $40 for a pair. They're fake