OBD 2 codes PO300and PO 0131.What's this?

Question

I have a BMW 325i 2004 which have diagnosis codes PO0300, PO0131 and PO174. We replace the sparplugs and oxygen sensor but codes continues showing. It have a misfire problem . Also the automatic transmission is not changing smooth ,sometimes change at 4500RPM and this wasn't happens before.

Answer 1

P0174 is what the cause is this is vacuum leak or false air getting past the MAF (mass airflow) go to the oil dipstick with the engine running pull out the dip stick if there is a large amount of vacuum, you will need a PCV valve or what BMW calls a drainback valve, If not , go look around the MAF to throttle body look  for torn air duct, either way you have false air correct this and the BMW will be happy