one time after the car warmed up the engine revved up and down (between 1000-2000 rpms). I checked my coolant reservoir and it was completely empty. I filled up the reservoir and added some to my radiator. once the car warms up it no longer does the revving up and down. I think I only used maybe a little more than half a bottle. Do I need more coolant or is it a deeper issue?

 

If there is a lack of coolant in the cooling system then there must have been air. There is a valve fitted to the throttle body that is called the FITV (Fast Idle Thermo Valve), its a aluminum bodied, valve that reacts to changes in coolant temperature and changes engine idle accordingly. If there is any air, then the FITV can act up and cause a bouncing idle. If you had a bouncing idle and a lack of coolant, then filled it and the bouncing went away, then id say it was just the FITV reacting to the air. Make sure your entire cooling system is topped off and bled. Fill the overflow tank to the "MAX" line, top off the radiator and use the 10mm bleed screw located on the top of the thermostat housing to bleed the air from the system. You MAY not even need to do this if you no longer have the bouncing idle but its a good idea to completely fill and bleed the system to prevent it from coming back.

 

you can rent a coolant pressurizer and pressurize it and look for the leak