When the engine is started cold, it takes several minutes to reach operating temperature which is when the engine is running most efficiently. Vacuum is created whenever the engine is running and can be used to control one or more auxiliary vehicle options such as heater controls or cruise control, and is also used to control emissions systems such as exhaust gas recirculation, or EGR. It also controls vacuum for the distributor to advance or retard the spark, ensuring the engine runs as smooth as possible. Vacuum is supplied to these systems through hoses routed in the engine compartment. If engine vacuum was supplied to the EGR system when the engine was still cold, the engine would stumble or stall, and would do so until it reached operating temperature.
The thermostatic vacuum sensor is mounted in the intake manifold and uses coolant temperature to determine when the engine has reached operating temperature. Once it has warmed up, the thermostatic vacuum sensor opens and allows vacuum to flow through it to the vacuum-operated functions it controls. If the thermostatic vacuum sensor fails in the open position, it can be difficult to start the engine when it is cold and will run poorly until it warms up. If the vacuum sensor fails when it is closed, it may start properly but will lose power and run poorly at warm temperatures. It will burn fuel poorly, creating higher exhaust emissions that may fail a smog check. The engine light likely will come on when the vacuum sensor fails.
The thermostatic vacuum sensor is an important part of the vacuum system that allows the engine to run smoothly and efficiently. If it is not working properly, your engine can stall or not start and you can be stranded in an inconvenient or dangerous situation. Have it checked and replaced by a licensed mechanic as soon as possible.
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