I just bought a 2007 Mazda 3 hatch with an auto. When idling in drive I sit around 4-500 rpms and the car idles rough and kind of like surges back and forth. When these surges happen all my lights dim. The car was fine until I turned the driving lights and high beams on. Car idles fine in neutral and drives fine

 

Hello
If you notice that your headlights dim or fluctuate in brightness when the engine is idling, then the primary culprit is your vehicle's charging system, particularly the alternator. ... The bad news is that your alternator is not functioning properly. The problem may be as simple as a loose or slipping alternator belt.