was out polishing the car so i fired her up and let it tick over.She was ticking over sweet as a nut (just under 1000revs) until after about 10min or so then it stated ticking over from 1000 -750 up and down,then the car started missing a little bit as if it was going to cut out, but before i even revved it it revved itself to about 1500 revs and there was a bit of black shit comin out of the exaust,then it ticked over like it did before when it was going slightly up and down between 750 & 1000rpm,this has happend a few times now.It seems to be when it warms up it acts itself,sometimes when driving it cuts out and is a twat to start back up,and when it starts back up there is quite a cloud of black smoke and a smell of petrol. pls help people as im gettin to the point where i dont like driving it