i have a 2008 focus ST with bad idling could it be a coil as i have changed the cranck sencer and spark plugs but still doing it any ideas please

What is your question?

starts up ok when revs slow down from cold engine fluctuates and shakes like its going to cut out tick over goes up and down when I changed the plugs 2 were sooty black

What makes this problem better or worse?

i think its better when you do higher reves

How long has your 2008 Ford Focus had this problem?

2 weeks