Engine Cooling problem
1999 Kia Sportage 4 cyl Four Wheel Drive Manual 83500 miles

Last summer I had the following done to my 99 Kia
Sportage. Water pump, timing belt, spark plugs, wires, air filter, fuel filter, thermostat replaced. I live in western Colorado and as our weather started to heat up so did my Kia so 2 wks ago took it back in to have the thermostat replaced again because it was fluctuating. Since getting it back it has started heating back up. It seems to do it only when I am sitting idleing. I can run on the hiway with the air on and it does not heat up. Once I get into town I shut the air off and just sitting at a stop light it will heat up. Any ideas? Thanks