Can anyone help with this problem...my 1999 A4 1.9 TDI with 210,000 miles, has developed a hesitation when accelerating between 1500-2000 RPM, accompanied by lots of dirty grey/black smoke from exhaust. It then pulls OK over 2200 RPM with less smoke.

I have tried the following ...
Renewed fuel filter
Cleaned air filter
Diesel purged fuel system with Redex
Removed,stripped cleaned all injectors and refitted
Inspected EGR valve and MAF sensor and are clean
Tried running with unplugged MAF and no difference
Checked for fault codes- none found
Checked turbo vane control rod for free movement
Cleaned turbo internals with mr muscle oven cleaner
Checked for leaking boost hoses

All to no avail...help!!!