Hydrolyzes 3-hydroxyisobutyryl-CoA (HIBYL-CoA), a saline catabolite. Has an indirect role in endocytic membrane trafficking. May have a function in protein biosynthesis in mitochondrial small ribosomal subunit (By similarity). 3-hydroxy-2-methylpropanoyl-CoA + H2O = 3-hydroxy-2-methylpropanoate + CoA + H(+) Amino-acid degradation; L-valine degradation. Belongs to the enoyl-CoA hydratase/isomerase family. Mitochondrion-specific ribosomal protein mS47 subfamily.