My E39 530d (2001) started to behave sluggish tendancies symptons: very slow response to acceleration power reasonable at 1/2 throttle, dire at full throttle significant loss of power above 3750 rpm better performance when engine cold.
I disconnected the MAF - the symptoms improved. Diagnosis: the MAF had died.
I sought an OEM replacement for my Bosch 0928 400 468 airflow meter. Result: part number has changed to 0928 400 527 and cheapest was £175 + VAT
Looked at far Eastern alternatives on eBay - got scared off by mixed experiences (see my previous post)
I decided to buy a Pierburg alternative which is just the insert (no housing)
Once I had sourced a security Torx bit, the replacement was a doddle (2 screws) and required very basic DIY skills.
Result - it is now A1 again and the cost was £61 delivered with VAT.
I'm sure they make the alternatives for other models too - my recommendation is they are well worth a try and they are reassuringly made in Germany.
I hope this saves someone else time and money.
David