ls400 Engine Code P0121 and P0120 - 2000 LS400

[otherworldliness]

We recently ran into P0121 and P0120 engine codes, and had the Accelerator Pedal Position Sensor replaced, and that resolved the problem for a short while, until the car is showing the same codes again. The problem tends to happen when the oil gas level is too low (below 25%) or too high (above to 85%), and now, it is happening regardless of fuel level. So, we are thinking about replacing the TPS sensor, and seeing if the problem would go away once for all.

Looking at the official Lexus repair manual, it references a lot on Lexus Hand Held Tester. Since I don't own one, what is the best way to install the TPS sensor on my own? Are there any video guides on the installation (I searched YouTube, but they are mostly generic, not specific to LS400).

Any tips on addressing the P0121 and P0120 are greatly appreciated.

P.S.1 I mentioned about fuel level in the post, and I should add that when we put in gas, from time to time, there would be clear liquid (doesn't smell like gas) spewing out of a tiny hole not far from the gas filler. Not sure if it is related to the engine codes, but I am just throwing this extra bit of information out in case if any dots are connected.

P.S.2 The car engine would turn over (as in, yes, it does start when you turn the key). However, if the codes are active, stepping on the gas pedals will not translate to any movement. On its own, and once in gear, the car would move like maybe 1 MPH. Now, if the codes are not there (either by erasing the codes from OBDII or disappearing by itself), the car will be road worthy, although it is dangerous still. It is dangerous because the moment that the codes come back up, the car will immediately lose power regardless of where you are. You could be on a local road doing 35 or on a highway doing 70..and the power is gone.

[Exhaustgases]

https://www.amazon.com/Actron-CP9670-AUTOSCANNER-Trilingual-Screen/dp/B011P30EMO

With a scan tool like this that will show real time data, you can accurately position the tps to show the correct opening, I have done it before on other cars. I do gen 1 LS so I have not done so on an LS. If you really plan on trouble shooting this sort of tool is good to have showing such things as long and short term fuel trims and O2 sensor voltages etc. So its a bit more than just a code reader.