1990 Honda Accord LX - Heats up

I have a 1990 Honda Accord LX with 190-K Miles on it.

For the past two months the car heats up in city traffic.

1) On the highway at 65 mph there is no problem. But when I pull into
city traffic after a 1/2 hour highway drive the temperature gauage
goes up almost to the top.
2) I turn the heater to max and also put the fan on Fresh and Max,
this seem to stabilize the temperature.
3) I can start the car and keep it running on idle for hours and the
temperature is steady (the car does not over heat).
4) I have checked the coolant and it is full.

Any help is apprecieated.

Thanks