V8 4.6 Started Runing Lumpy

Hi, can any one point me in the right direction?

I was sat in my 95 P38 on the phone with it running when noticed white smoke from the exhaust, this didnt last very long, but since then it has been running lumpy. it has not smoked since, only on cold start up and does not drink the water so far.
Any ideas, be nice Iam new to this

mmmmmmmm the good old p38 as reliable as ever