What was found
ON FLIGHT 4212 THE CREW REPORTED THE AIRCRAFT PRESSURE DROPPED 3000 FPM WITH CABIN DOOR CLOSED. TRIED MANUAL PRESSURIZATION WITH ENGINE 2 & APU BLEED SOURCES. POSSIBLE STICKY VALVE. TRIED SELECTOR FULL UP 7 DOWN. THE AIRCRAFT LANDED WITHOUT INCIDENT. THE AIRCRAFT WAS REMOVED FROM SERVICE. PERFORMED OPERATIONAL CHECK OF THE MANUAL PRESSURIZATION MODE IAW EMB MM 21-31-00, THE OPERATIONAL CHECK WAS GOOD. NO DEFECTS NOTED. AUTO PRESSURIZATION STILL DEFERRED. CORRECTIVE ACTION INFORMATION PENDING.