I don't think there is any right or wrong on this, if your rig has done say 200k and you put a full set on for preventative maintanence then it is understandable due to there have been known issues. I personally would just change them when they go bad, but I might change the full set when that happens, just depends on how many fault codes pop up. It would also depend on what distances I would be traveling.
You could start a thread on a lot of components that you could put in to this category of preventative maintanence, oxy sensors, maf sensor, exhaust, valve clearances etc. all can affect mpg.
What we used to find, This isn't fact but people that drove with a heavier right foot had smoother more efficient engines, they would be looser, Rev more freely and just drove better. People that drive just hovering the throttle all the time would suffer with more splutters and a tighter engine that would feel less responsive. The old 8 valve VW golf GTI was a prime example, if it was driven from new by a very careful driver to me it just ruined the engine, the car just felt slow. Another exact same car driven by a more aggressive driver would feel a lot more responsive.
Seem to be three camps on the issue of COP.
1) Replace only dead coil(s) when code/CEL dictates.
2) Replace hunting for performance issue without CEL.
3) Replace all 8 as a PM.
Certainly replacing only dead coils will give tangible results immediately, for the least $$ at the moment of failure.
What I find most interesting are the testimonials of performance (running rough), long before code or CEL reveled a bad coil to be cause. Along with notable improving in performance with those that have replaced all 8. The implication here is, coils do weaken and rob engine of performance, before failing.
I do enjoy interaction with threads as they develop, just as much anyone else. But I find threads that focus on one issue or parts like wheels, lift, performance enhancements, COP, O2's, PCV, Fuel Injector, T-Body, T-belt, S-belt, MAF or wheel bearings etc. to be very interesting and informative as well. They also become one stop shop for quick information. As I find it much easier than searching through dozens if not 100's of threads of mechanical problems, which is very time consuming. Especially with needing to wait for each page to load up advertisements.
Good point on driving style. Those high RPM engine real don't like a light foot. My understanding is high performance engine are designed to run at high RPM, I know my 240Z was. My modified GTO big block (low RPM) with high lift and long duration cam. Would shake and rumble at idle, loading up the engine with unspent fuel and carbon. It (well I) just couldn't wait to jump on it, smoking the tires and blowing out that unspent fuel and carbon. But the 2UZ-fe is well suited for low power band use. I drive with a light foot as it's not a sport or muscle car. I do get on the HWY as often as I can, recognizing the benefit. Even flooring now and then to blow it out. I also use good fuel & 44K now and then, too aid in keeping gunk & carbon cleared out. But driving style has only a secondary affect on coils at best, which is the subject of this thread.
