I have a 2000 BMW 323CI. I'm having problems. When it first starts it is fine, but when it warms up to a normal temperature, I have a loss of power and it misfires. Sometimes when I first start, it's only fine for a couple of minutes.
The first thing you want to check is on the driver’s side, the intake manifold and all the plastic there is between the radiator and the engine. You may barely even see them without a flashlight and a little mirror. Check for vacuum leaks and all that plastic cracks, because if it has cracks, it leaks air and does exactly what yours is doing.
The other thing you should do is have a good mechanic put up a scan tool and check the MAF sensor, because a lot of times it’s the MAF sensor. The MAF will go bad on those and do exactly that. If it is that, take my advice and buy a factory sensor, don’t buy those cheaper ones made in China, because they just don’t work on a BMW. Have this inspected by a certified technician, such as one from YourMechanic if you need help. They will be able to diagnose your car’s loss of power and misfiring issues so you know exactly what should be repaired.