Q: Cold starting

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my 2008 Lexus RX 350 starts but idles for a second and dies. this only happens in the morning or when the engine is cold. any clue?

Hello, When you start your vehicle in the morning and turn the key to on, the coolant temperature sensor reads the temperature of the coolant and relays this to the computer indicating that the coolant is cold. The computer then knows that it needs to enrich (add more fuel) the air/fuel mixture at startup due to the change in air density. When you start the car, you will notice that it idles high for a period of time until the engine warms up. This is the enrichment cold start process. This is done with what is called a cold start injector or cold start valve which injects more fuel into the motor until the engine reaches a specific operating temperature. The computer simply feeds a little extra gas through the fuel injectors to start the engine and then maintains a certain amount of fuel supply to the motor until it is warm. In your case, it sounds like you may have a faulty temperature sensor. In most cars there are two of these - one to relay the temperature of the coolant and one that responds to the computer to tell it when it needs to enrich the fuel mixture at start up. I would recommend having an expert from YourMechanic come to your location to take a look at your vehicle and diagnose your cold start issue.

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