Hi i have just had another engine put in my s2, only now it won't idle you have to keep the revs up. On my old engine this was the same until it was warm, but now it cuts out even when it is warm it is also sounds rough on low revs.

I have checked the compression thats good also changed the plugs ht leads checked all pipes and wireing but still the same so any help would nice, mabye i just need it tunned...