under one's own steam

under one’s own steam (independently, by one`s own efforts, without help) — своими силами, без посторонней помощи; самостоятельно; ~ на голом энтузиазме

Example 1: For two years I published the quarterly newsletter under my own steam.

Example 2: He was able to go home under his own steam even though he was feeling very sick.
(IdiomConnection))

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This expression uses steam in the sense of "driving power," as in a steam engine. (Answers.com)