I have a 1998 Lexus LS400 with 90,000 miles and it has stopped working. I drove it fine to doctor's appointment and before arriving it began making a tapping/knocking noise. Stopped the car and when I got out of the doctors office it would not start. Had someone bring me a battery and it still would not start until I held the key on for a long ime and when it started it was hesitating and started making a loud tapping/knocking noise from the top of the engine like it had no oil. I checked the oil and it was fine. When I tried to push on the gas the car died again. If you let the car sit for a day it will start immediately but will still make the loud noise on top of the engine and you can accelerate it and it won't go away. Once you stop the car then you can't start it again unless you hold the key on for a long time. I am getting the following codes:

PO120 TPS/Pedal Position Sensor A Circuit Malfunction
PO340 Camshaft Position Sensor A - Bank 1 Circuit Malfunction
P1120 Accelerator Pedal Position Sensor Circuit Malfunction

Help me diagnose the cause of my cars problems.