can you fix this problem

What is your question?

Whenever i starts the car it vibrates a lot and after running for a few minutes it acts like it wants to cut off but it dont and after driving for about 5-7 min it starts to run smoothe but my mechanic says that it has a vaccum leak behind the motor and he is unable to find it because it is so small so can you diagnose the problem and refer me to someone who cn rectify this problem for me thank you.