Rover 3.9i Running Rich troubleshooting

Thanks PhilipA and everybody else for your help. Put my multimeter On the temperature sensor all seemed good as it was warming up. It was working down to 300 . Once it got up to temperature, and thermostat had opened readings Were all over the place jumping from 300 up to 600 back down to 250 just flickering all over the gauge. I will order the part Monday and fit it. If that fixes the problem fantastic, but I will still go through everything else that was mentioned just to make sure everything else is ok Thank you for the great advice. The first thing that was mentioned seems it was the problem.
Will post with an update when sensor has been replaced