Fix a leaking vacuum line on a Chevy truck by using the vacuum diagram to systematically inspect each connection visually for a leak. One method of finding and fixing leaks is to make a copy of the diagram and use a highlighter to mark each connection as you test it. Each line should connect to the correct fitting at both ends and remain supple enough to ensure an airtight fit while each plastic fitting remains in good shape.
As a gasoline engine operates it creates a vacuum that the automobile uses for the operation of many systems and in keeping the engine operating efficiently. Trucks with onboard computers continually monitor the vacuum levels and ignite a check engine light if there are leaks. Engines often show signs of vacuum leaks with a rough idle even if they do not have the onboard diagnostic system.
Some older models of Chevy trucks have very few vacuum hoses, making replacement of all vacuum lines with a few feet of the appropriate sized rubber tubing. Follow the diagram, and make the connections between fittings accordingly. However, emissions standards have increased the number of vacuum hoses that return unburned fuel to the engine and make replacing the entire vacuum hose system impractical. With these engines, use the diagram and testing equipment for locating any leaks you cannot find with the visual inspection.