Car was steaming out an EGR valve looking thing

Sounds like the heater control valve. Does it look like the picture? If yes that controls the hot water flow to the heater core. To repair it you need to remove it and replace it. Should screw in at the fitting with a vacuum hose on top and a larger hose to the heater attached at the bottom port. There are two types, one has the extra port, the other does not, they do not interchange.