Random Overheating At Idle

I have a 98' Lumina 3.1L w/ 204,000 miles on it. For a few weeks it has randomly decided to start overheating at idle. Sometimes just a bit over the middle, other times almost all the way into the red on the temp gauge. The only time it will stay at a normal temperature is if I keep the A/C on at all times (fans are on).


-The only way to help cool it down is to turn on the A/C or start driving again.

-The upper radiator hose is hot and the car always blows hot air if you turn the heat on at anytime.

-The cooling system was flushed about 3,000 miles ago when I changed out the original water pump as it had failed.

Any ideas on what could be the cause?

No easy answer here, do the fans come on at 222 degrees, not using the ac? Are there cool spots in the radiator core, any sludge or contamination in the cooling system, is there debris blocking the condenser? Was the system properly bled after the flush?