I have an NA and looked up the brake control diagram and its much different/simpler. but i was interested in what you said cause my car also idles rough sometimes, especially when my foot is on the brake pedal. my cars idle with my foot on the brake will sometimes drop low enough where it starts to shake like you said. but if i let go of the brake pedal, the idle will slightly rise to a more stable idle. so i felt like i maybe had a vacuum leak somewhere as well and wanted to know how to check/fix it. but your explanation really helped. i will try the same on mine!