dynodave

Help please, My 2005 E61 2.5D has suddenly developed a fault, it will not rev from tick over, very little power for a short while then eventually the revs will pick up and it runs almost normal above 2500 rpm, it seems to have a massive flat spot from tick over to 2500+.
Plugged it in and code "4030 exhaust backpressure sensor before particulate filter, signal" is displayed.
I have removed DPF cleaned it, refitted, exactly the same running faults as above.
With the MAF disconnected the car runs perfectly fine but with it disconnected engine management light is obviously on.
Has anyone got any ideas.
Thank you