The fuel injectors can fail and cause drivability problems. Often there is no Check Engine light and the failures can be caused by corrosion of the connector, clogging beyond the point of cleaning, and/or internal failures.
1993 Nissan 300ZX Problem Reports
Most Reported 1993 Nissan 300ZX Problem Reports
The exhaust manifold often warps, breaking off the studs between the cylinder head and the exhaust manifold. The noise may be most noticeable when the engine is cold.
If the car is emitting blue smoke from the tail pipe, from burned oil, be sure both PCV valves are functioning properly prior to replacing the turbocharger.