A broken timing belt on an interference engine (like the Fiero's) can cause serious valve damage as the pistons and valves collide. This requires a head rebuild or possibly even a new engine block if the damage is severe.
Therefore, the need for engine replacement depends on the extent of the internal damage caused by the broken timing belt. A mechanic needs to inspect the engine to determine if the valves bent or if other internal components were damaged. If only the timing belt and tensioner need replacing, the repair will be relatively inexpensive. However, significant internal damage could mean a costly rebuild or even replacement.
