The ignition packs seem to regularly go on Scenics - it wouldn't surprise me if this was the case here - they advise changing them in pairs I believe. They come as 1+3 or 2+4 - I guess if you can confirm that the problem is with one pair this would inidicate these have gone. I imagine you could confirm it by a) removing the leads of one pair - if no worse you have remove dthe leads from the bad pair - if the engine packs up - you have removed them from the good pair. To save paying for a new pair in case its not the issue, swap them over and do it again.
Tim
July 2008