Iduction Pipe question

[Zanimat]

Can anyone please explain why the induction transfer pipe and the inlet manifold on my E300D 24v (W124) engine is heavily coated with carbon - presumably from the exhaust?

 

[jibcl500]

Leaking injector seal,

jib

 

[BlackC55]

Take a pic.

 

[Zanimat]

Ah....I've put it all back together, now, as I needed to use the car; I dismantled it to gain access to the spill pipes which were leaking quite badly. So I can't oblige with a picture - but the bore of the transfer pipe & the entry to the manifold are heavily coated with about 2mm of carbon, especially in the adaptor piece between the pipe & the stub connecting to the air intake from the filter, which has a butterfly arrangement in it. Hope that's clear!