96 3800 code P123

Working on Mom's Olds 88 with 45000 miles. Started with stalling issue, so I changed the upper intake manifold (it was leaking) and fuel pressure regulator (leaking gas into vacuum line). Upon restart, engine ran until it came up to temp, then check engine light came on, resulting in code P123. Engine will run OK, then after hot restart, the engine runs real rough, and code P123. Any advise would be appreciated.

I believe that code is for the throttle position sensor. High voltage.

Thank you for the reply. We checked the throttle position switch voltage with jumpers installed and got some slightly erractic vlaues so we changed the throttle position switch (new one). Had no impact on the situation, and the car is still throwing the same code. Does anyone have an idea of what might cause this code other then the switch itself?