Subaru engine's are great! They sound like they are missfiring all the time anyway makes identifying a real one a little difficult. I felt it today for the first time sat around 3.3k revs / 60mph, its like a small 3-5 seconds of hesitation that you mildly feel on the throttle on steady throttle and the engine note changes slightly. Putting the foot down pulls it out of it as soon as boost comes on and it revs up smoothly, but putting the throttle down around 10% when it's missing results in no acceleration and you can feel the hesitation until it suddenly bumps out of it.

My brain says coilpacks or MAF since it doesn't appear to be boost related (boost leak) or spark plug related (not under load, not continuous)... I'd probably lean more towards a coil. Are the coilpacks a common fault on scoobs?

 

What year is your car?

 

oops! Bit of vital info sorry. '97 Type R. Could be either jdm WRX or STI coilpacks.