Hi, I have a 2004 Audi A8 with dual fuel pumps in the rear. The vehicle initially would start fine then would ocassionally fail and misfire, then it got worse and worse, I even got to the point when it stops itself sometimes while I wait on redlights - (quite rare) .I had it hooked on fuel pressure gauge which showed pressure - initially fine (3.5 bar), but after a while dropping.
Mechanic checked pressure reg - (all good).

Ideas ?