Do you know what the egr valve is, and if so do you know where it is?
The code might be being set as a result of the position sensor on top of it, or if your car is 96 or later the egr boost sensor comes into play. To find that you'd follow the vacuum line from the egr valve to it mounted up high about in the middle on the firewall right by the wiper motor. That being said, the sensor on it, or the actual egr valve may simply be gunked up and not be able to move the sensor smoothly. The one on the firewall that looks like a traditional map sensor is not serviceable, but the vacuum lines are!
if you have a haynes manual you'd be looking at page 12-23 for 94-95 aspires or page 12-24 for later years for those wire colors for part conformation.