my car only has 43k original miles on it, and this is my first real problem Ive had so far. after driving for a half-hour or so it starts losing power and sputtering (feels kinda like the 3000 rpm sputter, only continuous). It only does it when im driving normal on the highway with the gas barely pushed in. when it starts doing it i can push the pedal and it will drive fast and normal until i slow down and drive normal again.
my car is stock ecept for down pipe, cat back, and i have an apexi safc(which probably has something to do with the problem) I think i might run a little rich. I know the safc is not the greatest way to regulate the fuel, the boner at the shop who put on the dp talked me out of a power fc, he said it was over kill. Im in the process of buying a standalone to get rid of the safc.
any ideas whats wrong?

 

Mine did this for a bit when switching to the PFC, then disappeared after about a week of driving. I was told the ecu was "learning" and that the pulsing I was getting was the injectors firing irregularly during this phase.

I DO NOT know if this learning was the cause of my symptoms but it did go away after a week.

You may want to inspect your injectors for clogs or damage also.

Other than that I have nothing...sorry.