Surging 88 420SEL
Your idle numbers seem a little high, Thats why everyone keeps pointing fingers at the valve but off idle the valve has little on nothing to do with smooth running.
Even though you say the plugs and wires are new, pull the plugs and look for oil fouling and possibly closed gap , carefully inspect the cap for tracking as well as the rotor.
You should also check the coil for good spark.
Mike
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