Make sure the EGR valve is opening. When the engine is up to operating temperature, pull the vacuum line off the EGR valve and feel if there is vacuum to the valve. If no vacuum, then inspect the vacuum lines. Place the vacuum hose back on the EGR valve, and try to look on the underside of the valve to see if the diaphram raises up when you reinstall the hose. If the EGR valve is opening, then it might be clogged, and it's a good idea to replace it since it's 20 years old. When you do that, inspect the EGR tube to the valve for carbon build up, and scrape off if necessary. You might notice that the nut that attaches the tube to the valve has been cut along the corners of the hexed surface, and this indicates it's reverse threaded, so you'd have to turn it clockwise, as viewed from the tube looking into the valve.
