Hi guys let's see if you can figure this one out. My car is just not running right. It's low on power and sometimes will be a complete dog especially at low RPM to the point where I can notice it when shifting. The car is been like this often on for a couple of months now. The odd thing is when I fill up the car she seems to run like a champ smoother shifting more power and sounds a lot better. Any ideas? No it's not the 02s it's an open loop tune.

 

In-tank fuel filter loading up? Filling up agitates the fuel tank, possibly washing sediment off the inlet filter, then after a bit it "reloads", causing power loss.
You might have a fair amount of sediment in your tank that is covering the inlet screen. Filling up "uncovers" it causing good running for a while. Hope this helps.