Poor starting Vito

[zenman63]

I have found the 115 vito is having starting issues , buy that I mean it does not spring in to life it starts after short cranking, the auto key does this anyway, but when it fires the rpm is low for 1-2 seconds then it goes to normal tick over, like a change in note from low to high.
It seems clean from behind but I am seeing soot on the rear bumper and mpg is poor.
54k full service history.