So, I have now become a new fan of Seafoam carbon liquifier. After much careful research, I took the plunge and treated my Touareg TDI injectors with this liquifier by adding two cans of it to a half-full tank (50L of diesel). I then drove 100km to get the Seafoam pushed through the fueling system. I did get mild white smoke that dissipated quickly, and vanished after about 50 km.
While this is certainly a subjective assessment, my TDI throttle response substantially improved with Seafoam in the fuel, and the V6 began to rev much more freely, all within the first 25 kms of the treatment. I suspect I had substantial injector deposit buildup because the perceived improvement was very noticeable.
Emboldened by the tangible results, I pulled out the 9-year-old SnoTek snowblower. I ran the little single-cylinder four-stroke for five minutes on untreated gasoline to get it warm and listen to the untreated engine sound. The snowblower engine was pretty rough and noisy, with noticeable soot in the exhaust. I then poured a half-can of Seafoam into into the snowblower gas tank, and ran it for another 45 minutes. Sure enough, the rough-running engine smoothed out within 5 minutes, and the exhaust soot noticeably reduced.
After she saw the Touareg and snowblower results, wifey then did the same Seafoam treatment on her 5.4L Ford F-150 gasser pickup. Her throttle response immediately improved within the first 10km of driving, and her idle reduced from a noisy 800 rpm to a quieter 600 rpm. She says that the engine definitely feels smoother after the Seafoam. She did get clouds of white exhaust smoke for the first fifteen minutes, and then the exhaust became invisible again.
I got the Seamfoam from Canadian Tire at $12.99 CAD per can. NAPA here in Alberta has it on sale for $7.50 CAD a can until Oct 31.
If you decide you want to try it on your own TDI injectors, you have at least two different application options: A) run the Seafoam liquifier directly into the live fuel line while the engine is running (two-person job; look for youtube videos to see the process), or B) be lazy like me and just pour it into a partially-full fuel tank and drive as normal.
If you do the latter approach, I recommend getting your tank down to 1/2 full or 1/3rd full, and use two full cans of the product. This increases the Seafoam effective concentration, and should get you decarboning results within the first 30-45 minutes of driving.