Replacing oil filter ccv valve on BMW 1 series

[Pepperjack]

I have a 2010 reg BMW 1 Series 116i. Had some rough idling and engine fault light on and some smoking from exhaust. Fuel mixture running rich too. Got diagnostic code for air flow mass meter and ignition coil. Had these replaced and codes gone. Still having same problem so replaced plugs. It’s better but still not right. Rough idling and smoke still there. A mate said it is likely the ccv crankcase breather faulty. I know this is not an expensive part, but think there is quite a lot of labour involved.
What would this cost to replace and put right in specialist garage or BMW dealer? Any suggestions please?
Thanks

[helix402]

Afraid your mate is probably wrong. Common causes of your problem are faulty injectors, low pressure fuel rail sensor, worn out valve stem oil seals.