will not fire sometimes

I got a vauxhall astra 1.6 16v sxi 2004, the problem i got is in the cold morning i turn the key and the engine turns over fast but will not fire. You leave it a few minutes and tryed again and it will start. So i wanted to know if anyone has had this problem? I tryed a crankshaft sensor but still the same. It also happens when you drive the car for an hour and park it up then come back and try to start it but turns over fast but not starting, if i keep the trottle pedal to the floor and keep turning over it will fire but sounds like the engine is coughing then runs ok. I got no lights on dash and no codes stored.
any help welcome.
cheers

just a update, i have tryed a new e.g.r valve and still got the problem, I dont know if the coil pack is faulty now because i got a wire which is on its own and not going to anything? could it be the cam sensor? Can anyone help me to fix the fix???