when my car is hot only intermittently it will start idling very lumpy then gets worse very quickly.and just cuts out.then if i try to drive it judders and backfires!it will start again straight away but will cut out unless i hold the revs up.when i do this the fuel pump speeds up and slows down and the revs go up and down.if i leave the car for a while then it as if the problem never happened!any help appreciated guys, cheers.