After injector seals:

Freeze Plug at aft end of intake manifold - clean and seal around edge with silicone gasket seal.

Power Brake Booster - remove hose and plug manifold - if it runs better and you get manifold vacuum back, you have either bad check valve or blown booster diaphragm.

Manifold pressure sensor - unfasten hose to manifold and use vacuum tester (like MightyVac) to test. Pull about 15" vacuum and see if it holds - if not, diaphragms in sensor are broken and you need to replace the sensor - they are individually calibrated during manufacture and also include an aneroid barometer for altitude compensation.

Distributor vacuum retard - check with vacuum tester same as manifold sensor to see if disto diaphragm is broken.

Measure engine temp sensor and ambient air temp sensors with ohmmeter to verify they are good.

Check all wiring and connectors for continuity - clean all connectors and use dielectric grease when assembling.

Clean harness ground point on intake manifold - check for corroded or broken wires at the ring connector. Use OxGuard when re-fastening after cleaning aluminum with wire brush.

Generally, significant vacuum leak will make idle high. make sure that throttle plate is properly adjusted as well as the throttle switch. If idle is too high with engine warm, idle valve closed, and aux air valve hose connect plugged to intake, then you still have vacuum leak. If idle is OK, then problem is likely manifold pressure sensor or temp sensor or associated wiring.