during cold starts and when sitting at stop lights ruff idling begins the code that was given was po171
My car has an automatic transmission.
Code P0171 is set due to a system lean reading. While worn or misfiring plugs or coils can cause the issue, they typically do not. Most common causes would be a mass air flow sensor or even a leaking intake manifold gasket. If the engine is drawing in too much air from a leaking intake gasket for example, this can effect the air/fuel mixture and set a code. Another component not usually suspected with a code P0171 can actually be a cause. The Air Solenoid Control Valve. This valve directs air from the air injection system into the exhaust on cold start and running. This is an attempt to reduce cold start emissions when vehicles pollute the most. From age and carbon build up, the valve can intermittently stick open, causing more air to be injected into the exhaust. The additional air will cause the oxygen sensors located in the exhaust system to give false readings and adjust the air/fuel mixture based on them. This can cause a rough running and check engine light to come on. A certified technician will be able to diagnose the cause of the check engine light and fault code P0171 to find the exact cause.
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