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Q: Car idling up and down

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The car is idling up and down.

This is a common issue. My first instinct would be to look for a vacuum leak. Air going into the engine is metered so that the ECM knows how much fuel to add for a correct mixture. If you have a vacuum leak or unmetered air, both the mixture will be off, and the engine’s idle can race as it does with most vacuum leaks. The ECM will attempt to control this sometimes, which makes it erratic. Vacuum leaks can also happen in multiple places. I suggest seeking help from a qualified mechanic to verify this rough idle diagnosis.

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