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Q: Warm starting Problems

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The vehicle will start-up fine when cold it will run alittle rough. I can drive wherever I need to go. When I shut it off and let it sit for 10 minutes and it will start, but idle down, run rough, and stall. Will have to do that multiple times to finally get it to start and stay running. It only does it when its warm and sits.

My car has 105000 miles.
My car has an automatic transmission.

A: This sounds like a common sign of a failing...

This sounds like a common sign of a failing ignition coil. Components that contain heat sensitive materials include parts like coils, injectors, igniters, and some sensors. Every time you start the engine again the coolant flows, the fans turn on, and the temperature drops. The areas in and around the tops of the combustion chambers, the exhaust manifolds, and the exhaust components are hundreds of degrees hotter than the outside temperature under the hood. When this heat dissipates and is absorbed under the hood, it is trapped causing this cycling effect. Components like ignition coils are very sensitive to heat when they are beginning to fail. Ignition coils are coated with a varnish-like insulation that becomes brittle over time after being stretched then contracted repeated as the copper beneath them expands and contracts at a higher coefficient than the insulation. The insulation develops small fractures that open when heated and close when cooled. When open, they allow shorting of coil windings and decrease or eliminate the coil’s ability to function. I would recommend having an expert from YourMechanic come to your location to take a look at your vehicle to properly diagnose your ignition system.

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