Q: Engine performance - 1997 Nissan Maxima

If the engine is running as poorly as you describe, it will actually be cheaper to pay the diagnostic fee so that the correct repair can be made rather than to continue to waste fuel. Obviously, a poorly running engine uses more gasoline than it is supposed to. You could easily save $30 a month in fuel costs if the engine can be made to run properly without too many repairs. Of course, the cost to resolve (fix) your car’s issue(s) will depend on the exact fault.

There can be mechanical faults (such as uneven cylinder compression, leaky valves) that can be costly versus really mundane and reasonably low costs, problems like a disconnected or broken vacuum line, stuck EGR valve, defective spark plug wire, blocked fuel filter or similar "limited" issues.

As far as the injectors, while installed, the solenoid component of each injector can be tested and the mechanical operation can be tested to some extent, but the only way to test injectors (for blockage) is off the car flow testing on a machine.

Injector service is definitely a good idea here. Typically, on a car of your vintage in any major engine work, I would automatically send the set of injectors to a specialized lab for complete refurbishment, including flow testing and internal filter basket replacement at a frankly minimum cost of $17 per injector. Of course, the injectors have to be removed from the engine first.

But before thinking about that service, there are many more obvious and easy-to-do checks including possibly a compression test to see what the basic mechanical condition of the engine is, before assuming anything about the injectors. In your situation, I would have another diagnosis of the performance issues, so that you can make the best decision on how to handle this scenario.