My guess is fuel delivery at speed in 5th gear as I have a Peugeot Partner Combi which to me is a 'flash gits' Berlingo if you look at the design.
I'm told the engine runs slower in 5th gear noted by rev counter so what ever delivers the fuel may be the problem. Diagnostic at Citroen garage may establish the problem, unfortunately not cheap possible around £50 but it may sort out fault. You could contact Citroen see if they can advise possible faults that would cause the problem at least you're armed with info when you approach the Citroen agent / garage. Additional advice would be to put youre question in the CARS section not mobile homes.
www.citroen.co.uk
bob, February 2013
