Id try to find the vacuum leak first.

Do a visual first. Check for cracks in the intake hose, loose hose clamps, collapsed vacuum lines, dry rotted vacuum lines, etc.

Easiest way to find a leak if you cannot visually see it is to spray something flammable on the hoses and watch for the idle to increase. Easiest thing to use is a bottle of propane, or a can of starting fluid. Just be careful, go slow, and very easy on the fluid. Keep it AWAY from the distributor cap.

Could also be your brake booster. Unplug the vacuum line from the booster, and cap it. See if this helps the idle issue.