The hard starting and poor performance at low RPM suggest it is not VANOS.
Mass airflow sensor is a suspect.
Your fuel filter thought was also good, but would not likely cause hard starting. On an e46, the fuel pressure regulator is in the fuel filter, so you actually have two suspects in one part. If it is several years old, a new one is a good maintenance item anyway, I would put one in. I posted directions here.
Cabin_Filter