Now it happens at all RPMS? NOT the ICV then..
Not when you're only on the brake right? If it happens at high RPMS as well, I don't think any little vacuum leak would do it, maybe a leak at the intake boot as Dave45056 pointed out ..
Not sure about DISA, but I would just unplug all un-necessary vacuum lines and plug them at the manifold. I don't think a difference in intake runner length/volume will make it run rough really.. maybe a leak in the diaphragm but that would just be a little leak..
Sounds like it is running real rough.. Bad coil? Maybe let it run rough for awhile and check the plugs? or probe the coils looking for one with unusual resistance? (Since it's intermittent it sucks, but if it gets bad enough to the point it does it all the time, it should be easier to troubleshoot
)
Am I hurting more than I am helping?
Good luck!