I had been getting intermittent misfire codes, and a restricted performance code once.
These all cleared with my "Torque" app no problem, but would recur a week or 2 later.
On the advice contained in this thread, I had my battery checked. It was 6 years old, and measured 12.2v. I have installed a new battery, and no codes since, although I suspect I am due plugs and coils at 100,000+ Kms.

 

To [hardingb] . . . and [jagqueen] . . . Firstly, on behalf of the team, thanks for the courtesy of your "Thanks" clicks.

Mostly though a HUGE thanks for your feedback. This is ample and much appreciated payback for the time and effort invested by each on our team to prepare and present this write-up and supplements.

So often, with problem solved, contributors tend to disappear until they next need help. This issue is both so widespread, and has produced such unexpected, confusing, and even downright false symptoms, that bringing it forward in this fashion has highlighted how we can avoid these problems . . . and save unnecessary expense.

Regards,
Ken