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Q: Car idling rough and missing.

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My car is idling roughly and missing. It could be one of many things: the spark plugs, rotor cap, plug wires, or the throttle body could need cleaning, I am not sure.

A: A misfire will generally cause a rough idle...

A misfire will generally cause a rough idle, but you must find out if its one cylinder misfiring or a random misfire, this is were a scan tool is essential. If you can trace the misfire to one cylinder its usually a coil pack or injector but if its a random cylinder misfire your looking at air/ fuel delivery, vacuum leaks, dirty mass airflow sensor, "lazy" 02 sensor that doesn’t respond fast enough, or a fuel pump thats on its way out. Have a mechanic like one from YourMechanic check for codes and look at the real time engine data while its running.

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