hot running 190E

'84 190E which runs hot when idling at stop lights or in traffic. guage indicates temp is okay until the car stops in traffic or at stop lights. guage goes up above 100 and towards 120. begin moving and the temp goes down.

noticed today that if placed in neutral and rpm taken to 2000 it starts to cool better but still 100 or above. new oil, new coolant, correctly diluted 50/50. any ideas as to what me the cause or is this normal??? the outside temp is 33 and rising very slowly. this is cold here and it won't be this way for long. if there is a problem i need to take care of it before the warm weather sets in.

thanks very much

vincent