How to Use WD40 to Check for Vacuum Leaks in Your Car Engine
To check for vacuum leaks with WD40, start the engine and spray a small amount of the lubricant on the suspected areas where a vacuum leak might be occurring, such as intake manifold gaskets, vacuum hoses, and throttle body gaskets. If the engine’s RPMs change or the engine stalls, then there is a leak in that area. It is important to note that WD40 should never be sprayed directly into the air intake or carburetor.