What happens in/to the engine when a car surge during part throttle acceleration (not compressor surge, the jerkiness feeling during part throttle acceleration)?

I want to know what happens to boost and timing.

I've done several logs to analyse part throttle surging on my car and I could not see any significant deviations in NM (Block 120), requested vs actual boost (Block 115), Timing retard (Block 22 & 23) etc.

I've got a Bailey DV, greentop sensor and have tried the boostvalve (made it worse), played with the wastegate and all the N75s. My software has been loaded onto other cars with the same ECU code and they have no problems....so it is not software related.

Car runs smooth and strong during WOT. Increase in octane levels make NO difference to part throttle surging.

What could it be????????????

since they could be causing the car to run too rich or too lean during part throttle. Also need to check the maf sensor since it also comes into play.

BTW what is a Greentop Sensor?

MAF runs at 172g/s peak so it is fine.

I've logged Block 31....here is what happens during part throttle surging:

Lambda Factor Lambda Factor
TIME
STAMP
0.81 0.961 1
1.62 0.977 1
2.31 0.984 1
3.02 0.836 0.727
3.82 0.75 0.688
4.53 0.75 0.735
5.13 0.75 0.766
5.73 0.836 0.984

What does Block 32 measure? What is fuel trim? Is there any other block that also measures something similar?

I had a look at block 120 and I could see that the torque reading varied a little bit I'm not sure by how much it should vary to actually cause a noticable jerk (was usually one or two 2-3NM dips)

What chip are you running? Because some peolpe have noticed a surge during part throttle on the dbw cars since the ecu is fighting to keep the car running right and the boost level correct during that time. This was a big issue with the vw MK4's with the dbw, which ended up being fixed by using a different N75 valve to control the surge issue.

I've got a German chip - Tuning-Concept.

I've tried all the N75 valves and it didn't do anything. The chip worked on other cars with the same ECU so it is not the chip...must be the car, which is a DBW :(

Surging only occurs at 50-80% throttle and between 2500 and 4000rpm.