I have been having voltage issues ... starts at 13.5 and would go down while driving ...

I did the alternator DIY and changed the MAF as well ... the voltage is still unstable. Now, i'm at a loss as to what to do next ...

Can anyone chime in?

 

Battery? When was it last replaced? Do you have any extra electronic components that are not stock/added on? Any other issues before this happened?

 

Where is the voltage unstable - at the battery or on the gauge? You may want to check voltage at the battery and directly at the starter. If there is a difference between the two then you may have a problem with the wiring between the battery and starter/alternator. I have heard the 997's have a battery cable coupler near the battery that connects the cable and can get loose. Did the new alternator come with a voltage regulator? Is the voltage reading too high or too low - does it change when the lights are in the on position?

 

Good questions from code7. Tell us exactly what it happening before the change and now.

 

Any update? I'm having the same problem. Start the car cold and am at 13.4v at the battery (used to be 13.8), then as the car warms up (less than 10 minutes idling), it drops down to 12.1v at the battery.