Carlesburg complaint dept, blows dust from everywhere
Long time ago, but seem to remember a flex hose that used to fail under the nacelle slipper fairing, it connects the hi stage regulator to the pack valve and any leak usually means no muscle air for the pack valve to open at idle. However when you open the throttles the pack can open (T/O symptom) and at TOD when throttles close, so does the pack valve.
When you look at the hose (12" long) it looks fine (braided) but a simple leak test finds it has turned into a colander.
But I could be wrong!