Have a pair of 300 hour 500EFIs with top ends done last season. Last time out the starboard motor was fussy starting for about thirty minutes and then fired up and ran without missing a beat. I attributed this to vapor lock as it was 110 outside. Today the same motor is making sudden power fluctuations. It's 200-300 on the tach, but severe enough I can feel it in the boat. It's not breaking up, or a rhythmic surge. It may run good for two minutes, bad for one, then good again. It does it and most RPMs under load (on plane). No codes or alarms, all gauges as normal. Ideas?