it been happening for a long time i just changed the battery 2 days ago cause i thought that was the problem but its still the same
My car has 252491 miles.
My car has an automatic transmission.
This sounds like it could be two separate problems. You may have been on the right track with the battery, but if the voltage drops while the engine is running, that sounds more like a charging system problem. It might be functioning well enough to keep you going, but just barely. You should have the system load tested to see what it is putting out. As for the poor idle, the first thing I look for is vacuum leaks. Any air that gets into the engine without going through proper channels will lean out the system and make the engine behave badly, especially at idle speeds. check for broken hoses or fittings that could be admitting un-metered air into the engine. You can have both these issues checked by contacting YourMechanic. They will send a technician to your home or office to check out your engine idle and your charging system right there on the spot.
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