Look at some of the old posts by Arthur Dalton on troubleshooting and repairing the EGR system.

Here is a paraphrase:

You must check all the components of the system: the valve itself, the wiring to the SOV that sends the vacuum signal to the EGR diaphragm, all the vac tubing in between, etc.

You already cleaned the pipe. Also make sure the port in the throttle body or the intake manifold (at the end of the pipe) is also cleared out good.

Take the EGR valve itself off the exhaust manifold and clean it out good. Clean the valve seat and plug with solvent to get out all the carbon (watch out, messy job). Stroke the valve open with your Mityvac and while it's open blast the valve seat with solvent. Use your MityVac to apply a vacuum to the diaphragm to make sure the valve is stroking properly and fully, is not sticky or stuck, and to make sure the diaphragm holds vacuum and isn't leaking off.

Check all vacuum hoses and fittings in the entire EGR system for leaks, cracks, missing, etc.

Connect your MityVac to the vacuum outlet of the SOV that goes to the EGR (SOV aka switchover valve - a solenoid-operated valve) that sends the vacuum signal to the EGR valve, start the engine, and see if the SOV is opening when it is supposed to. If the SOV opens, you will suddenly see full manifold vacuum (like 25" Hg) on the gauge of the Mityvac. The SOV only opens on certain RPMs and/or certain conditions of engine temperature. You will have to read up to see where that happens. It is probably in the shop manual or in the WIS.

Lotsa stuff to check here... hope that gets you started. The EGR system is a symphony of a lot of separate parts and systems all working together, a malfunction of any one of which will render the system knackered. It is a process of logical elimination: for example, if the EGR valve holds vacuum, the valve is clean, and if it strokes properly, then you know you must continue checking further upstream in the system.

This process may take awhile (like days) because you have to check one thing, clear the CEL/trouble code, and drive the car to see if the CEL comes back on and the code reappears. It was taking my car 5 days for the CEL to come back on after I had cleared it. The pros probably have some way around this but I don't know what it is.

Make sure you read Arthur's posts; he knows WAY more than I do and I left out a lot of necessary information. I used his posts and the above procedure to ascertain that my pipe was stopped up and the port in the throttle body was also stopped up. Pete