Steady throttle issue

Hope someone here can point me in the right direction.

 

My 5EAT 3.0R demonstrates the symptom of what seems to be a very slight misfire or surging on a steady throttle.

 

I have data logged accelerator pedal angle, engine speed, vehicle speed and it seems that below 2000rpm at accelerator angle of 6-9 degrees this issue materialises.

 

In the vehicle speed trace you can see fluctuation of 1-2 mph but with the engine speed log (sampling 100ms) you can see revs change between numerous values from 1630 to 1710 over a period of 3 seconds which I think is changing the vehicle speed - is this typical/normal vehicle behaviour on a flat road? I can imagine it's the algorithm used by the ECU to hold 'constant' speed.

 

I think this is the surge/misfire I'm feeling.

 

There are no fault codes via the OBD port and the car has covered 70K miles with full main dealer service history.

 

Anyone know here vehicle speed is measured (wheel ABS encoders or transmission) and could a fault here be causing the fluctuation in speed.

 

Any ideas appreciated.

 

thanks

so you are having a deterioration in the linear feel of increased throttle ? Sometimes the TPS has a dead spot which you can measure with a volt meter and look for it to return 0 as you open it more and more every 0 is a dead spot. Mind you these are very minute but it could be a root cause of this problem or at least a different angle on the issue