range rover diesel no power from start?

i am after some advice for my friend, he has a 2.5 dse on a r plate, the problem is that from a standing start it has no power, you have to put your foot right to the floor then there is a 2-3 second delay with no movement or power at all hardly then it goes , this is alot worse when cold when it will hardly move at for even longer but when warm it is a little better but from standing start is still awful, it has been put on computer at garage and has no faults recorded any ideas much appreciated. if it helps sometimes when the car is started from cold it will start but show no revs on rev counter and when put in gear conk out completely then you will restart and will tick over and show on rev counter fine any help will be much appreciated many thanks