You need to check the EGR with the engine running. When you push it the engine should bog down which would indicate the exhaust gas is
getting to the right place. If it hasn't been cleaned in a while I'd recommend you take off the EGR valve and give it, and the port, a good
cleaning with a synthetic carb cleaner. They carbon up after a time and cease to function.

Vac lines can also develop small cracks that leak air in where it shouldn't be. It's a cheap fix just to get the right tubing and replace them all to eliminate that as a problem.

'89 P'up, 2.6 I-Tec, 488,000 miles and done... gone to the great beyond