So when in my brothers car we notice the idle drop significantly when the alternator is under load. Now it does this in my car, but not to the extent that it does in my brothers. It will idle spot on at 1000 rpm, turn everything on, heaters on full, lights, dipped and fogs. Then the idle drops to around 400-600 rpm, amazing it doesn't stall. Naturally he is trying to avoid this at the moment. But was just wondering if anyone else has incurred anything similar.