would over filling the engine oil cause the car to mis-fire?

 

i changed the PTU, thinking that was the problem, but still the same.

 

car is very smoky, would it just be cos the spark plugs are covered in oil?

 

or does it sound like something bad?

How 'over-filled' are we talking?

probably half a litre, to a litre at most

A litre is quite a bit considering sump capacity is about 3 and a half litres. What you may get is excess crank case pressure. This will result in blow back which is probably what you're experiencing. It can blow seals. So check under the car to sea of your crank case seal is weeping, as well as cam seals and sump gasket.

 

If you get too much blowback then you'll get issues with valves not sealing in their seat and you'll loose compression. But that would be after prolonged exposure to it I'd imagine.