Get the OBDFusion app for your smartphone or tablet. Buy the appropriate interface adapter that plugs into the obd2 port under the dash. Search this forum for a thread on the app written by Balidawg. Check the following separately when the engine is operating properly and then when it’s less powerful:
MAF (grams/sec at idle and 2000rpm)
Long term fuel trims (LTFT)
Short term fuel trims (STFT)
Intake air temperature (IAT)
Buy/borrow a fuel pressure gauge. Remove the plastic cover on the top of the engine and attach the gauge to the fuel pressure test valve (looks like a tire valve) on the fuel rail. Item #2 in the link is the cap for the valve. Pressure if as to be at least 50psi at all engine speeds and loads.
https://www.realoem.com/bmw/enUS/sho...diagId=13_0900
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