Ive had this same problem... but it was also bringing on the enigine check light..
Goes to fire but sounds like engine flooded and wouldnt start..
I changed fuul filter, plugs, new fuse box next to battery.. still no joy.
Took it to a mate of mine who is the dogs Balls... he was baffled but...
Turned out to be a dodgy switch at back of the iginition barrell.
Took one off one from scrappers (£50 from main dealers)..
Bingo !!!!! fires everytime first time...
Dont ask me why it was causing these symptoms i dunno... very strange but jobs a good un.
So check the switch at back of ignition barrell !!