88 grande marque egr valve

[mrfixit435]

88 grande marque, 5.0 liter, FI, Air,160K.
Recently started ideling rough, hard to start, choppy during normal driving, black exhaust.
Whats been done:
new plugs, wires, fuel filter, air filter, rotor, cap, ingition module, egr valve.

None of these helped. However, when the vacuum line is disconnected from the egr valve the idle smooths out and it runs fine. Any ideas what would cause this? Is there a passage or something in the air plenum that might be blocked or something along this line? Will it hurt anything if the vacuum line to the egr valve is left disconnected? Any thoughts, Ideas or suggestions would be appreciated. Thanks in advance for any and all help.

Robert