thermo valve

i have an 91 eclipse gs 2.0L non-turbo automatic.Does anyone know how to test the thermo valve to see it is working.I put vacumm into it with the car off and it leaks and i dont know if its supposed to do that since my car failed emmisions on noX.I checked the egr it works fine.I changed all the hoses and they dont leak.But in order for the egr valve to open the vacuum hoses go to the thermo valve so it wont open.DOES ANYONE KNOW HOW TO TEST IT OR KNOW ANYTHING ABOUT IT???