the engine vacuum is checked and leak locating by a vacuum guage....you place the gauge with the proper fittings in line with the line being tested then sqeeze the rubber lines to see if the vac changes...this is the only way ..using your ears is weird...using carb cleaner on these rubber hoses and other parts is destructive...then with this age the carb base gasket..
the egr may also be slightly stuck open...
those carb vacuum operated devices are known for leaks...
the engine mounts will cause an engine to move too much ,,,and the transmission mount as well....another problem I ran into was the motor mount frame brackets were worn where the bolt ran threw,,had to use a larger diameter bolt,,and file the holes slightly,, for a snug fit..
driving with tires out of balance will damage the front end ...wheel bearings ....etc..