1990 Buick Regal Regal

You have the wrong engine size listed. Your best bet, if you want to spend less money by doing it yourself instead of going to the repair shop, is to get a copy of the manufacturer's service manual. It will show where the valve is on your engine and how to test its operation.

The fact the EGR valve isn't working doesn't mean it's bad or it's the cause of the problem. Carbon could be blocking the ports so no exhaust gas can get through. A chip of carbon can be stuck on the valve's seat preventing it from closing. The vacuum hose going to it could have a leak or someone could have disconnected it.

The valve will be shown on the vacuum hose routing diagram under the hood.