Howdy! The EGR valve is located on the left side of the intake manifold. Pop off the hose on top, unscrew the flare nut on the front side, the big flare nut on its left side, undo two long bolts and ergo!
To check it: Blow or suck through the large flared port; You should get nothing going through. Then, hook a vacuum pump to the little vacuum port on top, pull it to -4.7 inches mercury and see if it free-flows. Gradually let up on vacuum and see how the flow restricts: If the flow shut-off is linear, that's good; Otherwise, no. If you get no flow at vacuum or flow without vacuum, you either can: Replace it ($150 or so...ouch!), do your best to swab out the junk with solvent, or...
I did this: On the bottom of the valve are two rivets holding the bottom plug in; File them off and drive the rest out of the holes; Then, get a long, slender drift or punch and tap the plug out through the side flared fitting (It's angled downward). Get a pick and gently pick out the carbon, picking it clean, including in the orifice (Gently!). When you're satisfied it's clean, dab some JB-Weld around the inside perimenter of the EGR valve where the plug rests, pop the plug back in and slam a roll-pin through the holes. Wait a few hours and give it a test.
Whatever you do: DON'T dunk the GR valve or sandblast it! You'll kill the diaphragm. Best of luck!