The throttle butterfly should sweep from about 70 to 80 degrees open then close and back open approx 1/4 when key switch is cut off. if throttle isn't sweeping when cutting key off and is giving e-23 then you have a possible ETC that has gone south. As i said earlier, this might be a job best suited for a CAT dealer as parts could get costly in a hurry. Let me repeat that. COSTLY! This problem is not for a parts changer as an injector holder can be as high as 1000.00 US. With proper software and interface, the dealer tech can check sensors and make quick diagnosis of unit. What we really need to know is the P code to narrow things down even further. With PC a tech can compare accel angle to throttle angle, fuel pressure reading, engine timing, stoichiometric mixture mass airflow voltage, O2 readings ect. Good luck and let us know what you find.