1991 Accord EX EGR valve

In an earlier post I asked about NOx problems. Since then I've done an
engine tune up including valve adjustment, new ignition parts and
checked the timing. Today I took the EGR out and cleaned it up. I
inspected the two ports it connects and although there was some old
cooked carbon on the walls they did not appear to be blocked at the
opennings. I used a pick and vacuum cleaner to remove as much of it as
I could see, replaced the EGR and repeated the vacuum test. Again
applying vacuum to the EGR slowed the idle but did not stall the engine
at warm idle. Also I could hear the valve click shut when I removed the
vacuum so I'm pretty sure it's functioning, especially since it moved
freely when out of the car.

I'm wondering if there can be a blockage further down in the manifold
lines? If there is how can it be cleaned out? The cooked carbon was
no more than a 1/32" thick at most on the upper walls but I did manage
to dig more out at the bottom of the manifold port.

Bob Warasila