07 Mini Cooper s turbo rough idle and smelly exhaust
 

Have a 2007 mini cooper s.
has a rough idle when cold and a bit of a miss. Seems to have a smelly exhaust gas also. I changed spark plugs as I thought this may fix it but still the the same. I was thinking either changing all ignition coils which look really old anyway. Or I have heard there is a variable valve controller solenoid that can cause this. Any help is much appreciated.