Grand Marquis V8-255 4.2L (1982)
Air Injection Control Valve: Description and Operation
Differential Valve Delay Valve (DVDV)
This delay valve, used on some vehicles, delays air bypass during periods of low engine manifold vacuum. During sudden drops in manifold
vacuum, DVDV delays operation of vacuum differential valve (VDV). A sudden raise in manifold vacuum will open check in delay valve.