FYI - this code has been covered many times in this forum and a simple search for the code using the search box would probably return many threads but i'll be a good guy and post this again ;o)

DTC23
Throttle position
sensor signal circuit
malfunction

- Throttle position sensor 2 output voltage has
been approx. 0.3V or less (open) for a
predetermined period.
- Throttle position sensor 2 output voltage has
been approx. 4.8V or more (shorted) for a
predetermined period.
- When the throttle valve closed position
learning value is excessively low.
- When the throttle valve closed position
learning cannot be performed.
- A malfunction occurs in the relation between
throttle position sensors 1 and 2.

Your problem is coorelation between sensor 1 and sensor 2 inside the throttle motor assy inside the throttle body or TPS as it is abbreviated as. The ECM looks at these sensors and expect a certain voltage and to see the throttle at an expected position when the pedal position sensors send thier signals to the ECM.
There is a voltage (signal) irregularity causing this code to trigger. It is generally caused by a couple of things
Either you have a bad relay in relay box (the blue one) or a bad throttle body sensor which means the throttle body would need to be replaced. In alot of cases the wires at the connector on the throttle body connector tend to break right at the back of the connector. You can pull on those wires and if any of them are broken they will probably stretch or pull out. I would check the relays and the wires first. If you find any problem there replace the relay and/or repair the wiring.
If you find no problems there then expect to replace the throttle body assy.
As for looking at the pedal position sensors? no need, that is a totally different code E-24, it is not related to this code.

It was mentioned about turning on the key and listening to the throttle body during power up? Well it will do a self learn process so you should hear it moving back and forth... its a kind of buzz/hum high pitched. If you hear that then it is trying to learn it's position but it still may have some sort of issue inside not letting it calibrate correctly.

Good Luck on your diagnosis

Listen to the ETC to see if it is actuating with key on engine off. If not swap the fuel pump relay with ETC relay third one down in blue box? Also check all your wiring even in black relay box under left step. Even though it is a TPS code there are several different causes which are rarely the actual throttle position sensors.