I just got back form my test drive and knock sensor problem has been fixed!
Please, if the knock sensor codes appear for your 1999 Lexus ES300 do not buy aftermarket sensors or an after market harness. That is what I did the first time around and ended up having to tear my engine a part twice. In order to make sure you're ordering the right parts you'll need to check the month you vehicle was manufactured. If it was built prior to August 1999 you're going to want sensor part number 89615-12040 (~$165 a piece). As for the electrical harness you're going to want to buy part number 82219-07010(~$30-$50) it is extremely important that you connect the right plug to the right sensor. The OEM cable has a sticker on the connector meant for bank 1, the bank 1 sensor is closest to the firewall of you car (closest to the windshield). I know these parts are expensive but I'm telling you that the $25 bundles are complete garbage.
This is the most intensive maintenance I've ever done on a vehicle and was able to work through it pretty easily. Just take pictures of all the hoses and good luck with that bolt on the rear of the intake manifold (literally the bane of my existence). While I had the valve covers exposed I figured that I would check the spark plugs and that revealed an oil leak into spark plug tubes 1 and 3. To fix the issue, I ordered a valve cover gasket kit that came with the spark plug tube gaskets as well. After that I replaced the igniter coils, spark plugs, fuel filter, transmission fluid filter and speed sensors on the transmission.
Torques:
Knock Sensors: 30 ft/lbs
Lower Intake Manifold: 132 in/lbs
Intake Plenum 32 ft/lbs
Throttle Body: 168 in/lbs
Transmission Filter bolts: 94 in/lbs
Transmission Fluid Pan Bolts: 46 in/lbs
The most important thing I'd like anyone reading this to take away from my story is to bring an OBD-2 reader when ever you buy a car from a private seller and test it, regardless if the CEL light is on or not. If I couldn't do this work myself, I'd be out over $1000 in parts and maintenance.
Cheers