I just joined this forum and was terrified to find that my recently purchased 320i was a dog.
But then, hang on a minute, it's a great car and the engine is smooth and quiet. It has a rock steady tickover and runs great. After reading through the scary thread a few times, I contacted BMW customer services, who confirmed that it had had the coil, plug & injector upgrade in 2012.
So, I feel happier. If I hadn't read that thread I'd have been none the wiser and continued to love the car.
Ring BMW with the reg. and see if it's had the work done and then you can make an informed decision.
Just my 2p's worth ...