Q: Rough idle 1999 f 250 super duty

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My truck has a rough idle that is the only symptom it runs and starts fine no rpm fluctuations.
The SES light is on and I have had the codes read twice and both computers say no codes are present.

My car has 256500 miles.
My car has an automatic transmission.

If the check engine light is on, but literally no codes are present, the meaning of that would have to be looked into. On your model, there is a possibility that that signifies a defective PCM. Generally, in a diesel rough operation could be due to a bad tank of diesel, dirty injectors, incorrect idle speed or timing, exhaust restrictions, too much variation in compression across the cylinders, vacuum leaks, a defective or clogged fuel pump or fuel filter, and failing electrical components. I would recommend that you request a rough operation/rough idle diagnostic and the responding certified mechanic will perform the required diagnostic steps to get this resolved. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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