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Most older vehicles are equipped with a device called an idle stop solenoid that works to close off the throttle when the key is turned off. It prevents engine idle from continuing once the fuel and air stop being delivered to the engine. Fuel-injected cars don’t have this type of device. With fuel injection, the fuel goes to the injectors via an electronic pump, and the injectors are fired electronically, so when the key is turned off, there is no fuel delivery.
With a carburetor, there’s no electricity, so even when the ignition is turned off, the engine still rotates a bit, taking in air and fuel. Even though the car ignition has been turned off, there is still enough hot carbon in the engine’s cylinders to ignite a bit of fuel and create problems.
If your car’s engine keeps going when you park, you may have a problem with your engine idle. Engine run-on can often be due to a faulty idle stop solenoid. If you’re experiencing related symptoms, get your vehicle checked out by one of our expert mechanics.
If your idle stop solenoid is faulty and you experience engine run-on, it can be harmful to your engine because it interferes with the normal “cool down” phase. Your fuel economy will also drop. Have your idle stop solenoid replaced soon if it is deemed faulty.