Why does my 1995 impala SS run hotter when idling causing the Temperature needle to move close to the red but not overheat?

Engine is running slower at idle, therefore water pump is running slower and water is being circulated at a slower speed and there is no air flow through the grill to the radiator Try flushing the coolant and replacing the thermostat. This usually helps or solves the problem. If it doesnt then your radiator is prbably clogged and not properly dispersing fluid through it. You will most likely have to change the radiator. It is possibly the coolant temp sensor is not quite right. It could just be several things. Try the flusing first. Good luck.