Connect a regulator to your air pump. It is important that you keep the air intake regulated at about 3 pounds. Too much pressure could cause even more vacuum leaks.
Turn off your automobile's engine. Attach the hose from your air pump to a part of the vacuum fitting, so air pressure can flow into the intake manifold. Begin to apply air pressure.
Spray soapy water onto various areas where your engine vacuum may have sprung a leak. If you see bubbles forming, that means air is being forced through the wrong place, and you have found your leak.
Check other engine vacuum areas with the soapy water as thoroughly as possible to make sure you do not miss any leaks. It would not be surprising that there could be more than one leak in the vacuum. While you have the air being forced through and your soapy water ready to go, find all the vacuum leaks at once and save yourself the time and hassle of having to do the whole process over again.
Mark any vacuum leaks with a Sharpie or paint to make sure you can find them again. There are a several parts that may need replaced to fix a leaking vacuum. Once you have pinpointed any leaks, your next project will be fixing them.