Q: Car idling rough after replacing alternator

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My car is idling very rough after replacing alternator

My car has 161000 miles.
My car has an automatic transmission.

After replacing the alternator, your vehicle’s ECM will need to go through a "relearning" process whereby it will take a day or two for it to relearn the computer’s parameters and adjust. If by replacing the alternator, the battery was also presumably dead at some point, this will cause the ECM to need to relearn some of the fuel injection memory related to programming, fuel curves, etc. When this happens, you will notice a bit of rough idling and potentially, loss of power until the ECM relearns all of this information.

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