Rather than try to explain it all I took a video.....


I assume it's a plenum issue, as if you look in there is quite a bit of shiny oil coating the keg, is there a reason why spraying parts cleaner in it while it's sputtering makes it south out for a second or two?

 

Sounds more like a toilet flushing than a motor.......

Will it just not rev out? If that's the case, remove the front O2 sensor from the cat, see if it runs any better. It'll be louder....