if the injector had an electrical issue, ie open short or ground, I would expect to see a code for that. Otherwise, it could have a mechanical issue or clogged, dirty, whatever... just as you swapped coils as a test, you can do the same with a suspect injector.
That said, your symptom doesn't sound like an issue with one cylinder, it sounds like a second or two of no power would spread across 25 to 30 revolutions of the engine, all four cylinders down on power... so I'm looking at something that effects all four, but doesn't throw a code. Ignition side, I would probably see codes. Fuel/air side is a different story. A momentary loss of fuel pressure would not throw a code, but seems unlikely. A throttle position sensor could be inaccurate but I wouldn't think it would be that repeatable. MAF slow to pick up on a rapid change in airflow maybe? Give that a cleaning just to say you ruled that out. Something flaky in the throttle by wire system maybe?