Having a minor issue with my 2009. Sometimes when I upshift, I get a little "burble" or "stutter" between 4-4.5k rpm that feels like a misfire but disappears quickly.

I assumed this was caused by bad coils/wires/plugs so I replaced the OEM coils about two weeks with BHR coils along with MSD wires and new NGK plugs. The little stutter still persists but not all the time.

The only system I know that is wrong with the car right now is the secondary air pump....it failed several weeks ago but hasn't been a problem.

 

Could be the SSV or VDI not opening all the way or getting stuck. They're staged to open at a certain RPM.

https://www.rx8club.com/series-i-tec...ht-load-76505/
https://www.rx8club.com/series-i-do-...lenoid-190364/

Do you notice it happening on WOT only? What about cruising at low load and slowly increasing RPM?

 

It happens mostly on light loads as I'm going up through the gears, shifting at about 6K. Seems fine at WOT.