93 Safari 4x4 with intermittent EGR failures

Need help with 4.3L HO "W" engine problems.
This puppy has 224K miles and began to throw EGR codes whenever the idle was rough, or sometimes at highway speeds.
I've done this so far:
Replaced air cleaner, plugs, wires, distributor cap and rotor, solenoid-type EGR valve, oxygen sensor (was really fouled up with soot) and cleaned the PCV valve.
Added 20oz of pro-grade Techron injector cleaner to about 15 gal. of gas - van runs somewhat better on the road but it still idles very rough and emits smelly fumes. At times the engine continues to run a second or two after ignition is turned off.
Will appreciate all suggestions other than junking it - unemployed right now.
FatPat
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