9 times out of ten EGR problems are caused by bad vacuum hoses or clogged passages. Hi mileage cars are notorious for throwing this code. Take EGR plumbing apart and clean out all passages and orifices. Don't use solvent on EGR valve or diaphragm may be damaged. Get out as much carbon as possible from head and plumbing passages, they should be extremely clean and free flowing. Use wire tools to get small passages, and tube brushes and solvent for larger ones. Use new gaskets for re-assembly; vacuum leaks here will present other performance problems.
The EGR Modulator works along with EGR Valve and Vacuum Solenoid to control the amount of EGR flow into the engine. EGR flow cools the combustion temp and reduce NOX emissions. Vacuum lines from the EGR and vacuum solenoid go to the modulator.
The picture in my facebook post: http://www.facebook.com/photo.php?fbid=472075606173934&set=a.276330489081781.57564.186477864733711&type=1&theater shows the modulator, EGR valve and vacuum solenoid, this should help you find it on your car
Robert Grove, ASE World Class Technician, 1996 Automotive Hall of Fame