2009 Cooper s
93k miles
just had the HPFP replaced about 6 months ago

Car started throwing CEL today with rough running issues.

I pulled codes with my scanner, got the following:

B2AAA - Body
P0300 Random/Multiple Misfires
P0303 Misfire Cyl 3
P0304 Misfire Cyl 4

The rough running came on abruptly today when my wife was trying to pull away from a stoplight.

I know we need to do the walnut shell blasting on the valves - I am sure there is quite a bit of buildup. But would carbon buildup be something that comes on suddenly like that?

Any insight is appreciated.

 

Same codes on my MCS in October (55,000km).
Added an injector cleaner, high octane fuel and worked it towards the highest rpm range and no fault since then.
The BMW garage mentioned that this was due to poor gas quality.

 

You can start with process of elimination. make sure your engine has oil to begin with. swap coils and see if the misfire move. if not, pull the plugs and see their condition. while the plugs are out, shine some light in the holes and see if there is liquid or anything else. if all seems clean and nice, do a compression test.