M112.912 CEL on
 

My dad´s C240 with the M112 engine is a model year 2000 and has about 100k miles on it. Because it ran rough and had the CEL on he had changed all coils and plugs about 2 months ago. Everything fine until yesterday when the CEL was back on and the engine partially misfired until a restart. However, the engine light stayed on. I went to have the codes checked: P2053 on zyl 3. and P2055 on zyl 2. Code 2050 is also present.
Since the coils have already been exchanged where should we start?

Thank you in advance,

reinhard , vienna