This is my first post on here so I apologize if I'm putting this in the wrong place. My 06 vibe 5 speed has had this issue since i bought it and I'd very much like to fix it. mileage is estimated to be well above 400,000 miles if that matters. The car runs drives and shifts very well except for this one thing: at around 4k rpm and above it has this strange almost bucking that happens and it gets worse with more RPM. I know what a slipping clutch feels like and its not that. The best way I could describe it is it feels exactly like I am taking my foot off the gas and putting it back over and over again, even though my foot is still. I had two other of these cars and I've never experienced this. The car is perfectly driveable as is but I know the 1zz engine makes more power at higher rpm so it just kind of sucks not having much power due to this. I have other cars for this purpose, but I do occasionally drive this one in a spirited manor but this issue makes that sort of frustrating when I have to granny shift to avoid higher rpm. I am considering replacing the fuel pump and filter assembly thinking maybe it could be starving for fuel due to a likely original 400,000 mile fuel filter. I will also probably clean the throttle body and report back. If anyone has any ideas as to what this could be, or if I'm barking up the wrong tree please let me know. Thanks.
**Some more pertinent information:
I replaced the spark plugs with OEM denso 3324 and new air filter
No engine codes other than the obligatory p0420. (it has a new cat and OEM oxygen sensors)
The engine runs fantastic otherwise and has no blow-by and burns zero oil.
