2001 Ford Expedition Engine Over Heating

I can drive on the inter-state in the city everything is fine. Then sometimes when I stop at a traffic light the temperature gauge just jump to hot, it does not rise from med gauge to hot it just jumps. I turn off the engine and restart it everything is fine. Had it scanned ( OEM code P1299) probable cause low coolant, coolant replaced, Drive belt off it was not off, and fail cylinder head temperature sensor which was replace. Same problem continued, let it set over night and started up the next day and drove for short trip engine was out the temperature gauge did not jump to hot. The next day when shopping in town stop at a traffic light and the temperature gauge jump to hot turned off the engine restarted it temperature gauge back to normal but engine light came back on and I still have the same problem. Had it scanned again the same code came up P1299. Don't know what to do?