Whistling sound coming from underneath hood. Engine runs rough during idle.
This sounds exactly like the symptoms of a vacuum leak. When the engine inhales air through an opening it is not supposed to is a vacuum leak. The whistling sound is due to the air being drawn in through a small hole. The rough idle is due to the fact that the engine is receiving more air than fuel. I would recommend having a technician, such as one from YourMechanic, inspect your engine for vacuum leaks. Most likely it will be a hose with a crack near the air cleaner, or intake manifold.
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