Furthermore:
Idiomatic usage is actually giving the verb a sense of "while/as" so actually it's identical to the adverbial function semantically, the trouble is conveying this in translation forces us to classify it differently.
"yürüye yürüye gitti" (He went by walking)
"gele gele böyle mi gelir?" (As it comes/As it could be, is this what it came as?)
Nouns however are far more complicated as there are many many (see what I did there) usages, to add to Gemmenita:
Her yan ağaç ağaç. (Every side is tree-tree, Trees everywhere)
yavaş yavaş kalktı. (He got up slowly, as you can see nouns and noun-like words(adverbs, adjectives etc.) when duplicated do not take "-e")
Gözü mosmor olmuş. (His eyes were purple(as in he had a black eye) This exemplifies perhaps one of the most odd features of Turkish, intensity of certain words can be furthered by duplicating the first syllable and by adding a seemingly arbitrary consonant. If there is a pattern to it I am unaware, sorry.)