Check and replacement
1. With the engine warm, remove the spool (indicated by an arrow).
2. With the engine idling warm, put your finger on the spool hole. The absence of vacuum indicates contamination of the spool or hose. Replace dirty or damaged hose.
3. Stop the engine and shake the spool. If there is no knock, replace the spool.
4. To replace, disconnect the spool, noting its orientation.