BMW E90 N53 cold start shaking and code 30E9
Why does a BMW N53 shake on a cold start?
The most common cause is a leaking injector. It enriches the mixture of the whole cylinder bank, so the other cylinders in the bank get too lean a mixture and start misfiring when cold. The symptom often lessens once the engine has warmed up.
What does fault code 30E9 mean in the N53?
30E9 indicates ageing of the NOx catalytic converter and does not necessarily mean an actual fault. A misfire code also does not always point to the cylinder where the fault really is, so parts should not be replaced at random based on the code.
Does replacing spark plugs and coils help N53 cold shaking?
Not necessarily. After replacement the shaking lessened for a while but soon returned, because the cause was in the injectors. The condition of the injectors should be checked first, for example with an injector test or by reading live data from a cold engine.
What else can cause N53 cold running problems?
The high-pressure pump can cause a long start or misfires without a fault code; the fault only shows up in live data. A leaking valve cover gasket can also cause shaking when cold.