Check Engine Light comes on, code 0403

Hi, I have a 97 Nissan Quest GXE and there's 87,000kms on it. The check engine light came on and when I checked it out, the trouble code is 0403, and 0203 came on also. Does that mean there's something wrong w/ the closed throttle position sensor? Is there a switch in the sensor that needs to be replaced or is there just some tinkering that needs to be done to fix those trouble codes?

I need someone to help me out w/ this as the engine knocks under load. It actually happens more when the engine is hot. It even happens using 89 Octane, but it's worse on 87 Octane.