Trouble starting

[stefcio007]

Can't figure out why. Some days it will start with minimal key turning, perfectly. Other days it will take two tries, and quite a while of waiting.
Makes no difference if the car is hot or cold.
When it has trouble starting, really bad, I can hear it cranking fine but the engine just won't splutter into life, nothing.
It's very random though. It's bugging me because it become something worse.
Any ideas?

[Stanton]

relay 30

[stefcio007]

Might also add that lately it feels like it's about to die when idling sometimes. When I accelerate it doesn't happen. The car was juddering yesterday but today it's back to normal.

[stefcio007]

relay 30

Can't see it anywhere.

[patmould93]

I get the same sort of thing except it's particularly bad when it has been warm but hasn't completed cooled down yet. Sometimes it starts up and dies a couple times and so I have to put the foot down for it to idle initially... no idea