Check Engine Light-EGR VALVE

So i went into the shop and had them diagnosis my 95 pontiac bonneville se vin k non supercharged and they came across a egr code. Bought a used one from lima auto and worked fine for 4 days, the next day the check engine light came back on, next day it was off for another 4 days and it just repeats this cycle. I'm getting sick of the check engine light when it comes on. what can i do to keep that light off. When the light comes on and when it is off the car runs the same, perfect. what can it be or what do i need to do.

Thanx.