head gasket

Could be misfiring due to cyl no.2 might be getting coolant into it from the blown headgasket-try retorquing the head by specs and see what happens-don't work do an engine compression check

If you see antifreeze leaking outside, it should not be affecting how the engine runs, but it's more common to have leakage between the coolant and combustion chamber. There is a test for that. I call it the "sniffer" test. It involves drawing air from the radiator through a glass cylinder with two chambers partially filled with a special dark blue liquid. If combustion gases are present in the cooling system, the liquid will turn bright yellow. A cooling system pressure tester can be used to pump the system up to 15 psi to check for external leaks.