Shima if you are still having egr issues.
The egr opens at higher speeds, normally over 40 mph. This to dilute the air fuel charge in the cylinders to reduce Nox emissions.
When your symptoms and cel showed it seemed to happen on longer drives. What I believe is happening is the egr is hanging open, this is why your engine runs bad, vacuum leak at lower rpms. The computer sets a code when the egr is open at low rpms.
The egr solenoid does have a filter, I see it in the picture. The solenoid is just a switch. It should normally be open, vent egr side thru filter. When powered on the vent should close and route vacuum to egr. Powered off should open vent and bleed off vacuum at egr.
So if you have a vacuum guage with engine warm guage on egr vacuum signal port of solenoid, long hose up under hood and wiper blade, go for a drive. Watch guage above 40 mph maybe faster, 35" tires, guage should show vacuum. Slow down like coming to a stop guage should 0 vacuum.
If that is your results your egr system is not at fault.
It could be your cat. If you have excessive back pressure the egr can be held open. That pancake cat is original and TBI motors aren't designed well enough to keep the cat alive, not like modern engines.
Get an o2 sensor bung plug, drill and tap for ⅛" pipe thread. Thread a brass nipple with ¼" hose nipple. Put a ¼" fuel hose with a pressure guage 0 to 10 or 15 psi. On a hot engine rpms to 2500, you want to see no more than 2.5 psi on guage, I like 1.5 to 2.
If you see higher you have a restriction somewhere in exhaust system. My money would be on that cat.
2nd possiblity is carbon bits from the exhaust passage in the intake getting in the egr pintle and seat.
Hope this helps and if I confused you please ask for clarification