98 F-150 Low Temperature Input

I have been getting a check engine light for several months. The latest code is 117 (Engine coolant temperature circuit low temperature). In the past I have also gotten code 125 (Insufficient coolant temperature for closed loop fuel control). The engine sometimes runs rough when first started, but it seems OK now. I have replaced the temperature sensor (temp gauge worked OK before and after) and thermostat. Can anyone give some advice as to possible causes that a person with modest mechanical skill can address? I can't get inspected with the light on.