BMW Questions? Ask a BMW Repair Expert for Answers.
Hello. I will try to help you with this. I will provide the instructions for replacement of the spark plugs but a misfire can be caused by many reasons and a code reader might be needed to diagnose this problem. The first thing to check would be to see if you have bremi or bosch coils installed on this vehicle as you are getting to the spark plugs. If you see bremi then most likely you have a bad coil but a bad bosch could be likely as well. We have a know issue with bremi's so let me know if you find them. You will see the name on the top of the coil at the connector.
It could just be spark plugs, or you could have a leaking injector, or a mechanical defect in the engine like a bad valve. The first step is to suspect the coil. Find out what cylinder has the fault like misfire in cyl 3 and then swap that coil to say cyl. 1 to see if the fault then moves to cylinder 1. If it does then you know it is a bad coil. You can also do that with a fuel injector say the misfire is in 3 and you already moved the coil then swap the injector to cyl. 2 and see if the misfire moved to cyl. 2. Also it would not hurt to change the spark plugs if they have not been changed.
Switch off ignition.
Hello. It is always a good idea to let the vehicle warm up before starting off to prevent engine wear. Their are other two things it could be beside the items I described earlier. The VANOS unit could be failing-this would take a dealer to diag. The check is to unplug both the inlet and exhaust solenoid valves on a cold start to see if it runs good. If it does then the VANOS is not working properly and the fix can be a bit expensive. The other item is also expensive and would involve the HVAC's or hydaulic valve actuators (camshaft lifters). The sometimes bind under cold start and can cause a misfire issue on cold start. These items are for your information as the basics should be performed before faulting these items. The basics would be spark (plugs/coils) ,fuel(pump pressure/regulator/injectors), air(no air leaks, mass air flow sensor, clogged engine air filter). If the problem is good when the veh. warms up that might be the best thing to just let it warm up. Also one bit of advise I would have is to perform an oil service even if it is not due--if the lifters are binding sometimes this will help with the problem. I would also double the oil changes from the normal reading. Thank you and let me know if I can help you further.