Rough idle

Truck starts but isles extremely rough. Timing belt hs s not been checked for tdc. Hsve been told that #3 cylinder is bsd but I have strongly disagreed because the engine 2, 5 is supposedly a noninterference engine. Can a timing belt out of tdc cause poor idle as well as a knocking noise. Have heard that the timing belt out of tdc can csuse strsnge engine noises snd mimic poor compression. Supposedly all the other cylinders are fine.