tick over but want rev,trafic dci 100?

i have a renault trafic dci 100.it will start and tick over but wont rev.if i put the ignition on and undo the bleed screw diesel will come out,do it up again then it will start and rev ,its bit slowly untill 2500 revs and then it revs on fine.it seems to be electical because if i flick the ignition off and on when reving it wont rev again untill i stop and bleed again,if anyone has had and solved this problem i would be greatfull for advise