Are you low on coolant? Is there air in your cooling system? This could make the temp gauge jump around. One of these comes in handy to work the air out of the cooling system to make sure you have it full; https://www.amazon.com/EPAuto-Radiator- ... B01I40ZQWE
When was the last time you replaced the coolant? If you use the sealed funnel to fill the system, watch for bubbles or a tiny steam of bubbles coming out of the funnel once the air has been bleed out of the cooling system with the engine running. If you continue to see air coming out of the coolant, it could be a sign of a leaking head gasket or a cracked cylinder head. If the engine has been over heated it is highly likely that the head gasket is leaking or the head is cracked. You may also have an electrical wiring issue but check the coolant in the radiator first. The coolant used in these cars should be pink in color. If the color is not pink then you have some more problems as it either has the wrong antifreeze in the car or it could be a sign of compression leaking into the cooling system which can change the color of the coolant.