While driving at highway speed my 2003 Chrysler Voyager started "popping" under acceleration and would clear up when i would take my foot of accelerator pedel. Then after a few minutes the van lost all power and shut itself down. After i came to a stop i tried to refire the motor but engine would start to turn over and then quickly stop. I turned the key again and watched the water temp gauge move into the red and warning buzzer went off. after letting engine cool down i check coolant level and found to be very low. added 2.5 gallons of anti-freeze to radiator and tried to refire the motor once again, this time the motor fired without hesitation but began to run rough at idle. Drove straight home and notice while driving the motor would run smooth but would run rough at an idle. My husban checked the spark plugs and wires and is pretty sure they'er fine. He also check the condition of the plugs and also the gap. We're not sure which direction to head next. Do we check compression? Head gasket? or something eles? Any insight on this mater would be greatly appreciated. Thank you.