OK I doubt a vaccum cleaner would generate the required pressure and if it did it would initially start the pistons moving. In any event, some inlet valves would also be open or partailly open allowing the air to leak out the inlet system. Instaed
a) Have someone hold there had over the end of the exhaust pipe when the engine ahs been started from cold (so nobody get a burnt hand) and see if you can see smoke coming from other parts of the exhaust.
b) If this doesn't work do the same thing while the car is on ramps and run your hand along the exhaust feeling for leaks.
In doing these test be very careful to avoid breathing in any exhaust fumes; do the tests as quickly as you can and keep your head away from any fumes.
Most leaks can found by looking for holes in the pipes when the engine isn't running and listening for where the odd sounds are coming from.