PO123 on '98 Dodge Dakota. 3.9L, V6
 

This started about a month ago. My Dodge came up with this error code and the engine began to idle erratically and wouldn't change gears at the correct speed occasionally. Not only that, but the throttle was acting up while driving and kept revving high and dropping to normal. It also kept stalling, if I tried to stop at a light or a sign while in drive. To this day, I have replaced the PCM, the TPS, the IAC (Using Advance Auto Parts IAC), and cleaned the throttle body. It still has the issue and was even taken it to a shop before the PCM was replaced and they saw the PCM was getting a bad signal once the TPS signal reached it. The TPS was emitting a perfect signal, however. This is a real stumper, what could be causing my issue? Is it just the wiring?

If you're getting a stable voltage at the TPS but OBD-II is showing a varying throttle percentage, then I would definitely start chasing wires. You should end up with something like 0.9 volts at idle (OBD-II may show 0 to 5%) and 4.3? volts at WOT (OBD-II may show 80 to 100%). OBD-II may be able to show actual TPS voltage to compare to a multimeter.

So you think it definitely could be the wiring? Heaven help me, if I need a new wire harness because my grandfather couldn't find one online. My Diesel Technology instructor is going to help me test the voltage, to see where the wire could be bad.

Harness doesn't exist except for junkyard. You don't know till you test the circuit, possible there's a frayed wire or bad connection or a short somewhere.

I'm gonna bring this up to my Diesel Technology teacher, he can definetly help me find the bad wire.