'87 560 High Idle - EZL vacuum

[Rick Hesek]

Hello all,
I was in the process of finding the cause of my 1000 rpm idle when I pulled the vac line off of the ignition control unit. The idle dropped to normal (~ 650 rpm).
I thought this vacuum signal was for electronic control of ignition advance. At idle, should there be vacuum at this port?
I will check the vac connections to make sure I don't have a crossed line pair, but what else could cause this?

Thanks,
RH