When your car engine hesitates, rattles and shakes when you idle, it might be the result of air entering your engine. This will cause your car to run inefficiently and is typically caused by a vacuum leak. Finding the vacuum leak in the safest manner possible can be tricky, because it can be caused by a broken or cracked vacuum line, a leaking manifold, a leaking carburetor gasket, loose or missing carburetor crews, and open carburetor fittings.
Start the vehicle and leave the engine idling. Maneuver your hand over the choke housing, cupping it to create an artificial choke.
Notice the idle speed after cupping the choke housing. If the idle speed increases, you have a leak.
Take a length of vacuum hose and place it by your ear. Place the other end near the running engine, and listen for the leak. Make sure you don't come close to the fan or the fan belts.
Mix cleaning solvent with auto transmission fluid, about 50-50, in a garden sprayer or a similar device. Spray this mixture all around the intake gasket. You'll notice an increase in engine speed, if a vacuum leak is present -- along with white smoke coming out of the tailpipe, from the automatic transmission fluid.
