Im not to sure what a Leberon is but it sounds to me more like a "Boost Cut" problem, the engine ECU (Engine Control Unit) via MAP sensor (Manifold Actual Preasure) senses the amount of preasure or boost output by your turbo, this will be set to a predetermined maximum, when this maximum is reached the ECU will either cut the spark or the injector pulse thus inducing the "Jolt" you talk of.
My guess it that the vacuum/preasure line to the waste gate actuator is possibly broken or has been tapped into to increase boost.
BUT...... if the above replys are correct, try some av gas that should stop detonation
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