Q: Car is is idling low, poorly, and is getting bad mpg.

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A couple months ago my car threw a check engine light for both upflow o2 sensors. I went to a mechanic that I've known for 20 years that hasn't ever steered me wrong and he replaced both of them. How ever every once and a while the check engine light comes back on and it reads those 2 upflow o2 sensors. After a short while the light will go back off though. The constant symptoms no matter if the code is there or not are: *The car idles at around 500rpm *At stop car will shake and rpms will drop to almost stall and bounce around before going back to 500rpm *Very poor gas mileage *I believe slower acceleration by a little I'm also pretty sure i have an exhaust leak by the sound of it.

My car has 126000 miles.
My car has an automatic transmission.

Based upon the symptoms you are describing, it sounds like you may have a faulty camshaft position sensor. The camshaft position sensor is a magnetic sensor that monitors camshaft speed to regulate ignition timing and fuel injection timing. It gathers and sends information about the car’s camshaft speed to the car’s electronic control module. This information is used by the computer to further calculate the time of ignition and the timing of fuel injection required by the engine. When this is not working properly, you may experience a drop in power, poor idling, poor fuel mileage and problems starting the vehicle. As the sensor begins to fail and gets worse over time as the signal it provides to the computer weakens. I would recommend having a professional from YourMechanic come to your location to diagnose your camshaft position sensor.

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