A slow-leak puncture on a tire could be many things, but nine times out of 10 it is caused by a foreign object, such as a nail or a screw that has poked a hole in the tread somewhere and is still lodged there. This is easily remedied in a matter of minutes,allowing you to get to a service shop where the tire can be properly patched.
Make sure the emergency brake is applied. Jack up the car at the corner with the slow leak.
Remove the tire from the car. Look over the entire tread for the foreign object. If no nail or other object can be seen, it likely fell out. In this case, spray the tread with soapy water from the spray bottle and look for bubbles. These will indicate the location of the hole.
Put the patch from the repair kit on the tire tool and push it through the hole with the tool.
Remove the tire tool by pulling it out slowly and gently. The plug should remain firmly stuck in the hole.
Replace the tire on the car and lower the car. Drive to your nearest tire shop to have the tire properly patched.
As when using any tools or making any repairs to an automobile, exercise caution and wear all proper safety equipment.