Motor stutters around 2000rpm, '04 m54 e60 525i

[woodyteacher]

Just purchased an e60 '04 525i auto with 230,000km. The motor has a stutter around 2000rpm. Under normal driving the motor flips 200 revs up / down around the 2000 - 3000rpm mark. This occurs irrespective of load. Give it a boot full and it revs fine to 5500 without a hesitation.

I have read a bunch of threads with similar issues and have made changes accordingly:

I have changed:

Plugs
Coil packs
Charged the battery
Removed and inspected the DISA valve
Replaced the VANOS O rings and rattle rings
Checked the poly pipe from the PCV valve to the oil separator for cracks and leaks
Cleaned the VANOS soleniods
Disconnected and reconnected the MAF

I have scanned and cleared the stored codes - mainly linked to the CAN bus - then taken the car for a good drive to only have no codes reappear. The CEL has not come on at all. I'd look at fuel pressure, but it runs fine at higher RPM, so I don't think it is related to fuel or injectors. Could be a vacuum issue, but it idles well. It almost feels like it's an issue with the kick down, but again no codes are thrown on the auto.

Before I give up and take it to my indy I was hoping the collective brains trust might have an idea.

Cheers

[jtbgonesailing]

Has the fuel filter ever been changed?

[woodyteacher]

Thanks for your response jtbgonesailing ... no, not to my knowledge. I discounted the fuel filter and injectors as it revs well without hesitation above 4000rpm. If it was starving for fuel at 2000 rpm surely the same would occur at 4k, or am I (quite possibly) missing something?

[jtbgonesailing]

You've pretty well covered the gamete of potential causes, especially with no error codes. The fuel pressure regulator is integrated into the fuel filter assembly. At your mileage, you are certainly past due for a changeout of the assembly. Stranger things have happened.