Hoping someone knowledgeable can chime in...
I thought I had a vac leak which was causing my idle to be a bit lumpy (varies by about 25-50rpm). Went through all the old pipes, deleted some of it even... made sure there is no leaks. When putting the car back together I forgot to plug the sensor back in and I thought I had cured the problem as the idle was steady.
Went out in the car and it ran OK apart from wide open throttle where it stuttered ran smooth ish. Realised I hadn't plugged the sensor back in I did so and immediately the annoying revs were back to varying.
Also had the car on the rollers a week ago and the car made stock power but it appears looking at logs of other cars to almost be lagging - which is why I went looking for vac leaks. It does appear to have no power down low. I have experience with exhaust leaks before which has caused this pre turbine but I have had a feel around when cold and can not feel any leaks.