slow acceleration and not revving past 3000

[inderpal123]

hi, i ve got a vito 108 cdi y reg 2001 model. The problem is it went into limp mode (i think). It does not rev past 3000revs, but it was still ok to drive. 70 mph max. Then a couple of weeks after that the revving slowed down and the van accelerates very very slowly. The engine sounds fine still moves back and forward but very slow, also when it hits 3000 revs you get some white smoke out of the exhaust. ( not too much). has anyone got an idea what it could be? i would be very greatfull thanks.

map sensor has been changed too
air filter changed

could it be the injectors?

does anyone know a mobile mechanic that works on vito's and does the computer diagnostics. I live in hounlow, west london area. thanks!