Car back / miss fires on part throttle

ibiza_95

1.8T MK2 Conversion
When im on the motorway mainly in 5th gear, i have my foot only slightly on the pedal and every now and again the car will really jerk, it feels quite a powerful jerk too which makes me think it could be a backfire as opposed to just a missfire, and also pops a bit at the same time.

It does it in other gears sometimes, but not as much but then im guessing thats cos most other gears ive got my foot a little bit further on the acc pedal.

Does this sound like anything similar to any one elses issues? Ive not got standard management thats the only thing, i use an MBE ECU, the cars done it since i bought the engine (Transplanted into a mk2 ibiza)

The car runs off the following sensors connected to the ECU:
Crank position, throttle position, boost control, MAP sensor, Lambda, Coolant temp, Air flow or possible air temp, one of the two... and thats it as far as i can remember.
And then connects obviously to injectors and coilpacks (bolt on should it make a difference)

It doesnt feel hesalthy one little bit when it does it, really slows the car down

Cheers
 
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