Ever since it has been cold out my battery light will be on when I first start the car until I get it warmed up. I took it and had everything tested and the place said a few of my diodes (SP?) were going out in my alternator. The car actual has let me sitting once. I just bought a new alternator. My real question is could a bad diode in an alternator cause the car to idle like crap? When I bought the car it had an SCT Tuner on it but the glass was broken on it so I cant see it. I am sending it back to get it fixed next week. I want to have the car running perfectly by spring.