about to pick up a 94. the car while turn on but after about 15 min it will die. owner says that a mechanic said the opti was going bad. could this also cause the car to run sluggish(not enough power) i checked the block and it is a lt1 but seems like no power. also noticed that one of the plugs was sparking and it was hitting the exhaust manifold, could that be the problem? aside from all of that exhaust manifold has a leak and need the bolts replaced, where can i pick up a new set of manifold bolts?