If the ignition system is tight and not providing wayward sparks propane enrichment is a very good way to source vac leaks. You need to be able to hook up a length of hose on your propane dohickey or buy a propane enrichment kit from the local tool truck. Mine was $45.00 and worth it. When you have the propane bleeding off at a very slow rate you can pass the hose around gasket surfaces, vacuum fittings and hoses. You can also use it around your carb or throttle body to check for leaks at the throttle shafts. As the propane slips past the vacuum leak it briefly enrichens the fuel mix. The idle speed will smooth out and rise momentarily. Fuel injection plays a different tune because the Idle speed compesation motor (iscd/iscm) will quicky readjust the idle speed. Propane is a clean dry fuel source that will not mess up metal or painted surfaces like carb spray will. Water has other complications one of them being too much water sucked in a running motor from a large leak could lead to hydraulic lock (big ouch). Or cold water in/on a hot motor makes unhappy metal. Remember being told not to add cold water to a radiator on a hot engine?

Joe

 

Problem become is that a delphi system will only give you a split second to notice the variation, and using propans slowly can give you false idle speeds. The propane will be sucked intop the a/c system therefor making test null and void. Where as the water sprayed at the seals will not be sucked into the a/c and if there is aleak you will noticed the idle change. Water seems to work better than propane on smaller leaks also