Yeah, thats pretty much it Taco. Here is a pic of a Toyota ACIS manifold off an older engine. In the second picture you can see they use a vacuum actuator to open the butterflies on the secondary runners. When vacuum is low in the intake manifold plenum, the actuator opens up and opens up the secondary runners. To prevent this from happening at too low an rpm (not enough airflow to make the secondary runners worth opening), they use a vacuum solenoid valve. Below X rpm the solenoid stays shut and the actuator can never see low vacuum pressure. Its actually a pretty simple setup.
