The injectors and the computer determine the amount of fuel dispensed at each tick of the pulse. As injectors are simply solenoids, the mechanical components and the passage orifices wear over time. As the pulse width may stay the same, if the injector orifice enlarges from erosive wear, the amount of fuel flow each pulse increases. Outside of changes in the feedback from the O2 sensor, the computer has no way of knowing how much fuel is dispensed per pulse.
I would suggest having a service done on the injectors and also replace the O2 sensor. To properly service and check the injectors, they must be pulled and tested externally.
I’ll do that if my mileage or performance drops. So far I’m still getting 32 mpg with a six speed manual. And performance is great.