I have a 2000 Allroad 2.5 TDI TIP with 117,000 miles and I am getting problems with "juddering/misfire" after/during a high rpm run (>3000 rpm), accompanied by "grey/black" smoke. The best description I have had is that it feels like "driving over a cattle grid".
The juddering can occur once off throttle and then trying to accelerate again from a lower rpm. But going above 3000rpm in one of the higher gears, seems to be the trigger point.
There are no error codes and no drop in power until the misfire kicks in. I have a boost gauge installed in place of the voltmeter and this is not showing a drop in boost during the misfire (stable at around 15psi - is this even correct?), so I'm assuming overfueling??
Interestingly, if the car is placed into neutral and the rpm is allow to drop to tickover, then there is no judder when applying more throttle.
Items recently changed (some under warranty, to try and cure it): fuel filter, turbo, injector pump, gearbox, gearbox ecu, control injector, N75 valve.
I definately have a shot thermostat, as I'm only seeing a constant 80C.... this can't be contributing.... can it?
also, I do have a DTEK tuning box installed, but the problem is there with/without it.
Other than that, it's a great car..
Any thoughts most welcome.