Some diesel intake manifolds are notorious for getting clogged up by sooty exhaust gas recirculation, especially when it comes into contact with oily vapors recirculated in the intake tract. This one is from a 2001 Volkswagen Golf TDI I did some work on recently:
Attachment 2279
Attachment 2277
Attachment 2278

I cleaned it by igniting the hydrocarbon mass with a propane-powered "weed burner" torch:
Attachment 2283

...followed by compressed air (once the embers were hot enough air is all that was needed to spread the flames, and blow the hot embers out.)
Attachment 2282
Attachment 2280
Attachment 2281

Here are some of the charcoal bits that came out:
Attachment 2284
...in hindsight, I should have positioned the manifold so gravity would help the charcoal bits fall out, (but more on that in post #2.)

The torching (followed by scraping) was very effective in getting the inside of the manifold clean of all the heavy residue. Here are what the inlet and outlets looked like afterwards:
Attachment 2287
Attachment 2288

More pics coming in next post (due to 10 pic post limit)