easternjets said:When the coil packs fail they fail completely and you will have a noticeable misfire.
Coil packs fail because the older style get moisture inside them, they split and then they fail.
This is not quite true Nick, coil pack failure is not binary.
Sure, when they split, corrode and get wet they misfire. However when they dry out they can also return to working as if nothing had happened.
Equally, as they age they may not produce as high a quality spark from the plug as they should and this can lead to misfiring or hesitation when the most powerful spark is required - ie at high speed/WOT.
Regardless, its best to change them as soon as you can so you have a baseline from which to fault find.
Personally, I'd be surprised if the exhaust leak was causing any of the problems you've mentioned, especially if its after the post cat lambda. Erratic idles are often linked to post MAF vac leaks and fuelling problems (ie injectors, fuel pressure etc) although there are many others.
Good luck with the troubleshooting, I'm sure it'll be well worth the effort :thumb: