So, if you unplug the wires to the solenoid it smooths out?
If so that's eliminate the mechanics of the system and point to the control circuit.
Not sure if the EGR system is pulse width modulated or not, but that could account for the choppy vacuum reading you saw.
I don't believe there should be EGR at idle, I know on the older mechanical only systems there isn't. Might be time to crack open the FSM and read up on EGR operation.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
