Photoionization with synchrotron radiation and photoion-photoelectron coincidences are used to prepare C2H2+ with internal energy ranging from 0 to 6 eV and to study internal and collision energy effects on reaction with CH4. Absolute reaction cross sections are measured, as well as H/D scrambling and kinetic energy release derived from coincidence time of flight spectra. At high internal energy, the two main products are C3H3+ and C2H3+. The first one comes from a sequential dissociation of C3H5+ and/or C3H4+ products resulting from a long-lived complex reaction mechanism. The C2H3+ product, however, comes mainly from a more direct mechanism, namely, an osculating complex, but also results in small part from the dissociation of a long-lived complex, this latter channel increasing with internal energy. Two new product channels, proton transfer and H- transfer, are observed, appearing several electronvolts above their thermochemical threshold, in the region of the C2H2+ A state onset. Several hypotheses are proposed, which involve isomerization of the C2H2+ A state into vinylidene or H-bridged ions.