How do you check to see if the EGR valve is working?.?

I have a 93 Grand prix and my mpg has gone from about 22 mpg to around 15~16 ish the car isn't as quick as it once was their is no soot or anything at the exhaust tips. The O2 sensor is a year old and has about 12,000 miles on it the air filter is okay the fuel filter is okay I checked the spark plug gap and its fine. My car has the 3.1L MPFI engine it has the digital EGR valve with the three solenoids how do I test the solenoids to see if they are working and should I change the PCV valve as well?. the grommet is new but the valve is the original. I run 87 oct in the car the engine does not have anything wrong with it mechanically and the fuel injectors are working as they should the engine doesn't stumble or miss.