I have a manual 2013 Mini Cooper S with the N18 engine, and it had some pretty bad idle issues, so we took it to mini and they said the valve cover gasket was leaking oil into the sparkplugs causing the misfires. So we got the oil filter housing gasket, and the valve cover gasket replaced, but it still ran rough so we took it back and they replaced the valve cover too, because it was cracked. It's running back to normal now, except on cold starts. It misfires and I get these codes:
2774: 0x2774 Air mass, plausibility: air mass too high
2BC0: 0x2BC0 Mixture control: Mixture too lean
2EFE: 0x2EFE combustion misfire, multiple cylinders: detected
2EFF: 0x2EFF combustion misfire, cylinder 1: detected
2F00: 0x2F00 combustion misfire, cylinder 2: detected
2EE2: 0x2EE2 Misfiring, multiple cylinders: harmful.
​​​​​​I'm thinking that I might need to replace the spark plugs and ignition coils again after the valve cover was replaced, but I'm confused why the mechanic wouldn't do that and what happened with the mixture control and air mass. Thank you for any help.