hello all

ive just got a focus rs and its been fine for the last few weeks but over the last few morning, starting it from cold it takes ages and when it does it miss fires but after 20-30 seconds it clears and seems to run fine

also while drive it it some times misses and pops and bangs
i had the engine light come on the other day and had it checked and it said it was the catalist system but it hasnt got a cat on it, so im thinkin it must be the lamber sensor,

any help would be good