Ive got an bmw 316 compact

High possibility the maf sensor needs dervicing or replace. you can clea it yourself with electrical spray cleaner CRC brand. It is located inside the intake duct in a metal section. Do not brush or rub to clean. Use the spray to thoroughly wash off the sensor, It is sensitive and expensive to replace so be nice to it.
The spray will dry fast so don't use compressed air and don't physically touch the unit. Good Luck, Ned