Sometimes finding what it's not is half the battle, and after some diagnosis today, I still don't know the problem but I know what it is not.
It's been brutally cold here and yesterday with the salamander running I was able to get the inside of the unheated garage to about 20 degrees. Today I broke out the construction heater as well and with 140,000 BTU's of propane was able to get it to 40 degrees inside. That's as warm as it would get but it was better than freezing.
I ran through the basics, just because that is the first place to start. The static timing is still dead on and the dynamic timing is within spec. I did the timing belt 12K ago and replaced a bunch of parts, to include a new oil pump, windage tray, vacuum pump, and a
new turbo at 442,000 miles.
While the valve cover was off, I checked the lifters because they have been noisy with the extreme cold but none of them had collapsed or had any play in them.
With a multitester and the Bentley, I checked the QA (N146), needle lift sensor (G80), start of injection valve (N108), and crank position sensor (G28), all were within specifications.
I still wasn't satisfied it wasn't the #3, so I swapped it out with another I had on hand that only had about 10K on it and that tested fine.
It ran the same way with the same Vag-Com results.
While the #3 was out, I checked what I could of the piston with a new borescope and did not see anything out of the ordinary.
But, what I did notice was that the oil was down, like barely on the dipstick. I topped it off right before W386's trip. He drove about 300 miles all together and somehow 1.5 quarts of oil was missing. I checked the intercooler and found about 1/2 a quart, or just over 400ml when I measured it. I drained the intercooler before he left as well, so it was empty. The turbo came from BoraParts and was new 11,000 miles ago but the car sat for about a year with me only putting about 1k on it in a year due to having to fix the floorboards.
W386 says the car still pulls fine but he didn't drive it that hard so he really doesn't know. I'll tear the piping off it and check it in the next few days.
I doubt this is the issue but more of an 'also' deal, so I'm still looking for the original issue that's causing the rpm fluctuations and fuel imbalance. It starts just fine but is never smooth and runs rough.
Any additional ideas are most welcome. I'll post up some Vag-Com shots next.