Hose hanging down from center of engine is extremely vague.I tried leads and plugs , couldn't get one plug out but changed all others that seemed ok , I'm now thinking it's idling rough because exhaust has hole on , I have noticed something that may be related , underneath the centre of the engine there is a rubber hose hanging down , should it be attached to something or is it some sort of overflow?
Find out what is on other end and someone may be able to help