For early CAP, Chrysler was used manifold vacuum on engine braking.
CAP ran leaner idle mixtures, and lower idle vacuum than non-CAP engines.
To be sure the leaner idle mix was given enough time to burn thoroughly on decel, vacuum advance was used via a special valve. 1967 Chrysler Imperial CAP System from the Master Technicians Service Conference Session 241
This was later dropped on most automatic equiped cars.
