The TT has been fairly low down on the list of priorities recently but I installed a replacement refurbished K04 turbo on it last weekend.
Fortunately, putting it all back together didn't take anywhere near as long as removal and that included taking off and cleaning out the intercooler and all the pipework, along with dropping the sump and cleaning that out too. Luckily, the oil that came out was still pretty good so it was more just piece of mind that I wouldn't be sending crap through a new turbo. All fitted back up with new gaskets, bolts and crush washers etc.
Fresh oil and filter and then I cranked the engine a few times without firing, to make sure the new oil had circulated, before starting and letting it idle for a while.
Once up to temperature, I starting putting some revs on it and it all seemed to make the right noises until after a little while, it developed a misfire
It would clear itself once it returned to idle and as it was getting dark and cold, I put the tools away and went inside to sulk, confident that the turbo swap was ok but disappointed there was further issues.
For good measure, I compression tested the engine this week and that produced good results so that gave me hope that the engine hasn't sustained any internal damage due to the original turbo failure.
Had a bit more of an investigation today and the code reader showed a misfire on cylinder 3 so I swapped the coil pack with that of cylinder 1 to see if the misfire would follow it. Had the car running constantly for an hour or so, combination of idling and bouncing it off the limiter and of course, now no misfing
So I've swapped the suspect coil pack for a known good spare anyway and I see how it goes. If it's now the coil pack then it could also be possibly be the wiring loom for the packs, as that can be a common issue. Moving stuff around might've given it the jiggle it needed. Either way, it seems to be running so I think the general advice would be to "send it"