Rough idle

Hi, I'm one of the auto experts on RepairPal's Car Genius team! Great question, and the details you've provided are really helpful! On your 2010 Nissan Armada, what you are experiencing is called a hunting idle, where it surges up and down like that. The fact that it stabilizes in gear while remaining high at stops is a pretty classic symptom of a dirty or failing idle air control valve or a vacuum leak somewhere in the intake system. The fact that it settles down when placed in gear suggests the engine load is masking the issue rather than actually fixing it. A faulty mass airflow sensor or a dirty throttle body can also cause this type of erratic warm idle behavior on the Armada's 5.6L V8. It's worth checking for any stored trouble codes even if the check engine light isn't on, as there may be pending codes that point directly to the cause. Given that an elevated idle of 1,500 RPM at a stop can affect braking feel and fuel economy and can, in the long run, cause damage to other components I’d recommend having a qualified shop diagnose this sooner rather than later. If you would like to find a trusted, certified repair shop in your area, you can check here: https://repairpal.com/certified If you need more advice, or have any further questions about your vehicle, we’re here to help. Just give us a call at 877-913-1554