Toyota Repair: valve, 1990 toyota camry, nitrogen gases

Question
my car is a 1990 toyota camry and i have a 4-cylinder and my question is what is a EGR valve? and how much you charge to put one on?  

Answer
Hello Ramonia, welcome to my expert page.
The EGR (exhaust gas recirculation valve) is part of the engine's emission control system, it reduces oxydes of nitrogen gases which are harmful to the environment and create air pollution, what the cost is depends on where you live.