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High resolution (2-3 x 10$\mathrm{<mrow\; data-mjx-texclass="ORD">-3</mrow>}$ cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) Fourier transform infrared spectra of gas phase $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}$B and $\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}$B enriched and natural samples of BF$2$OH (difluoroboric acid) were recorded at Wuppertal and Richland. Starting from the results of previous studies}, it has been possible to perform the first rovibrational analysis of the $\nu 4$ (BOH bending) and 2$\nu 9$ (first overtone of $\nu 9$, the OH torsional mode) bands located at 961.5 and 1042.9 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) and at 961.7 and 1043.9 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) for the $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}$BF$2$OH and $\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}$BF$2$OH isotopic species respectively. In addition to various "classical" vibration-rotation resonances, large amplitude effects were observed for both the 2$\nu 9$ and $\nu 4$ bands. These result in a doubling of levels of about 0.004 and 0.003 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) for the 9$2$ and 4$1$ states respectively. The energy level calculations account for these large amplitude torsion-bending perturbations using the IAM- type method}, and for the "classical" vibration -rotation resonances.