take a look at the crankshaft pully with the engine running.
Does it wobble? When the engine is stopped can you wiggle the above-mentioned pulley with your hand?
If it does, the Previous Owner attempted to remove the crankshaft pulley by removing the big bolt in the center of the front of the crankshaft instead of the five smaller bolts that hold the accessory pulley to the crankshaft timing belt pulley.
Removing the big bolt and not properly reseating it can result in damage to the locking keyway which, in turn, throws the timing off enough to cause the engine to run like cr|removethispart|@p. If the damage is advanced, a new crankshaft and timing pulley is required.
Check that out first and let us know what you have discovered.