problem
On 1990–1995 M104, M119 and M120 cars the loom insulation turns to green dust. Misfires, no-starts and ghost codes follow.
Lift the engine cover. If the loom is sticky, brown-green, or the insulation slides off the copper in your fingers, stop diagnosing sensors. Every sensor on that engine is lying because its wire is a resistor.
Random misfires, sudden stall, ABS/ASR lamps, the climate fan going mad, and pulse codes that change every time you read them. A ‘new HFM’ will not fix a harness.
Replace the entire engine harness with a modern-insulation unit. Budget the part plus a careful afternoon; it is not a dealer-week if you are organised, but it is not a lunch break either. Do the valve-cover gaskets while you are there so oil does not attack the new loom.