Vivaro won't rev when cold?

I have the same problem on a 54 plate ex BT van, it won't rev up for 20 odd seconds, the van is driving me insane, I have changed everything MAF, EGR, injectors and various sensors adding up to a small fortune, I have finally given up, even Evans halshaw Vauxhall can't sort it out, any help out there before I burn it

Haydn
April 2016

mine does the same but only for 5ish seconds but when it does rev it is as if the throttle has jamed for about 3 seconds whats that about

craig
January 2011