I'm having a similar issue, sat in traffic the other morning and the car starts to wobble, no power, sounds rough from the exhaust note, get home, checks all plugs, work except for the far left hand one, try it on another pack and works, so plugs ruled out, moved the pack that appeared to not work to another plug, still not working so hey presto i thought, its "that" (points and frowns) pack there it is........go to the scrap dealer, get another for £15, put it one, still not working on the left hand connection, but it does work on others, What do I chack next??