I own a citroen saxo 1.4 westcoast, it has recently started misfiring and sometimes doesnt even start, it doesnt do it all the time, i can be driving it all the sudden it will start juddering and will cut out, when i restart its fine, sometimes when i go to start it just turns over then eventually gets going sputters and coughs then ones you give it a few revs it clears its fine, i took it to a garage and they pluged in a diagnostic machine and coudnt find anything wrong the mechanic also took it for a long drive and it didnt find anything wrong, it also cuts out when slowing down, any advice would be much appreciated