I agree with Suergoose9's description of the EGR and operation.

Apply vacuum to the EGR to see if you can see the diaphragm or stem move by using a mirror and a bright light. It should also hold a vacuum too!

Check out the gray vacuum valve on the drivers strut tower to see if it passes vacuum when engerized. I disconnect it and hook up jumper wires from the battery.

The ECU turns on the valve. If it does not see a resistance change on the sensor each time in so many timed intervals, it trips the Check Engine Light or the Check Emissions Light. Your choice?

On that gray valve I have found that there is a piece foam rubber, under a cap that you can pop off, it deteriorates into crumbs and plugs up a vent hole or passage.

I sucked it out or blew it out, I do not remember which while energizing it.
I replaced it with a piece of polyester fiber filling from a pillow cushion. Ask a woman about it. They always have some laying around for their craft projects.

In about ten years you may have to replace it as dust gets in there eventually.

If both items work then you may have debris sticking up the EGR either open or closed. By using a larger amount of rapid successions of vacuum it might dislodge any soot from the seat.

Removing and servicing is a little tough since it's down under the manifold but I have pulled one off an engine tahe was removed. The nuts holding it were not a problem to loosen. I hope you do not have to go that far into it!

Good luck testing things.

Phil