BMW 320 engine emits black smoke, shakes at idle and when the accelerator pedal is pressed

Q: A BMW 320 that was repaired was equipped with an N46 naturally aspirated 2.0L engine. After the oil leakage fault was recently repaired and the valve oil seal was replaced, the vehicle’s engine emitted black smoke, shook at idle and when the accelerator pedal was pressed, and reported a 4-cylinder misfire fault and a front oxygen sensor fault. Repeated consultations and repairs by multiple people could not solve the problem. Please guide me!
A: If a vehicle has a new fault after disassembly and repair, it is most likely caused by not paying attention to marking during disassembly and repair. According to your description, it is possible that the 3rd and 4th cylinder injector plugs are plugged in incorrectly, because only this possibility will cause the vehicle to produce black smoke and misfire related fault codes. Restoring the original correct connection should be able to eliminate the vehicle’s fault.