2010 PTT (I've had it for about 9 months). Ran rough with a bunch or errors and check engine right after filling up. I shut it down and restarted and everything was fine, no saved errors. About 2 weeks later same thing happened. Only this time it took several cycles before running properly and I was able to get a code out of it. Cylinder 4 coil. Since then its back to running normal. I have service history from Porsche and coils had been replaced July 2016 about 40,000km. I'm debating replacing all (and plugs) but 8 coils is pretty pricey especially if its not needed. Generally speaking whats the expected life time of the coils and should I just suck it and replace them all or just hit 4 and 8? Thoughts?

 

Coils just do not fail all that often. Failure is usually evidenced by a lack of continuity between the top and bottom connections. Heat is the big enemy and sometimes coil gain exterior cracks causing shorts.
My recommendation is just to replace the coils that have failed. Consider brands other than oem Porsche. Porsche does not make their own coils. They are purchased from outside vendors like Bosche and Becker. . Check RockAuto. Check eBay. I am replacing my oem coils with Becker high performance coils at a fraction of oem price.

 

I would replace the rear coils when doing the plugs on a service interval only, even if they don't fail. While it adds a few hundred dollars, they are the only ones worth it. The other 6 coils are easily replaced if they fail, even by the average garage mechanic.

Likewise, when replacing a rear coil, I'd go ahead and spend the $10 a plug and swap the rear plugs. Not worth the effort (certain not if paying someone) to wait until the maintenance cycle.

 

Imo replace all 8. Cost about 35 each. Replace plugs too. Have threads on rhis topic. Routine maintenance. Heat kills beru coils all the time.
Topics - coils, plugs.