I used to see over 13 (13.8ish)volts at idle. It has nothing to do with the tune, it has to do with the voltage regulator and the diode on the back of the alternator. I love how everyone always blames the tune first. . .
Well, one thing about that IS true.....the PCM does control alternator voltage on these cars. Whether that voltage is variable in the tune, I do not know...I have never seen a variable for that.
When the first alternator in my car went bad, I just outside of Columbia, MO driving home to Columbus, Ohio from a buisness trip. I had been getting intermittant camshaft position sensor codes for a few days, and a check charging system message off and on that day. It was also super hot that week. I knew that the alternator was on its way out, but I hoped that I could get home before it quit. No such luck. I was about an hour out of Columbia when I noticed the voltage dropping on the Livewire. I turned off all of the accessories and started looking for a place to get off the freeway. As I pulled off the Check Charging System message appeared, and the battery light came on at just over 9 volts. It died pulling into a gas station. Luckily, at the time, my car was just inside my extended warranty that I had bought and never used. I called them, and they called a tow truck. He loaded it on the flatbed, and took it to the closest authorized service center, which was Firestone. I told them what was wrong, but of course, they had to verify it. Once they did, they ordered an alternator (this is at about 4:30PM). I went and got something to eat, and waited for my car. They called me at around 6:30 (I think they closed at 6), and said that my car was ready. I picked up my car and hit the road, hoping to make up time getting home. I was maybe 15 minutes out and the Check Charging System message comes back. ...I was like WTF..now Firestone is closed...But, watching the Livewire, the voltage was staying around 14 volts....so I decided to just keep driving. Firestone had put the wrong alternator in, and it did not have the PCM charging lead, but it was internally regulated. I drove to Indianna with no problem, and got a room for the night. The next morning, it started right up, and I drove the rest of the way to Columbus. The day after I got home, I went to the local Firestone and had them put the correct alternator in. They were actually very skeptical about what I was telling thm, and kinda pricks about it...I almost had to go off on them in front of a bunch of potential customers....
