Just had the car back from a tuning company lots of work done map timing belt clutch etc etc, driving up the motorway slip road give it some beans then the car started like bumping & seemed to be hunting slightly & idling around 2000rpm, also the Rev gauge needle is bouncing all over the shop not giving a true reading when I drive over 3000rpm, I've been told it may be a vac leak, what's the best way to find out if it is & any advice on what I can do to eliminate other things