I wonder if you eliminated the ECU out of the equation and monitored speed and throttle position using an Arduino and having it make the adjustments based on throttle position (stepper motor to TB) and watch speed for cruise adjustements.

Code

run=1
throttlepos = tpSensor;

throttlePosAdjust[-1]=+0.3
throttlePosAdjust[-2]=+1.0
throttlePosAdjust[-3]=+2.0

while(run=1){

if(speed < targetspeed){
  speediff = targetspeed-speed
  throttlepos = throttlepos + throttlePosAdjust[speediff]
}


I digresss.

I do agree DBW isn't perfect. I have an annoying issue somewhere in the 10-15% range on my 300C. Occasionally she will act like I am at full throttle for about a half second. (only happens when I am taking off and I think mostly as I am making a corner). And it is a little slow to respond.

98,6Bolt,3"EXH,LINKV3,780cc,SD,SCM61@26PSI, 340LPH,AFPR,TSBOV,REARWB,FMIC,2"RAD(20/80/WW)