Citroen C5, temporary loss of pulling power

[Lane]

Hello from Belgrade (Serbia),

I have a 2002 C5 petrol/LPG, with an engine problem. Whenever I push the throttle a bit harder in low gears, the engine from time to time stalls starts to shake and loose acceleration power, after which I have to turn off the engine and wait a few minutes for it to become normal. It only happens occasionally. I am guessing that there is a bad spark plug or cable, but I am not sure..

It happens both in petrol and LPG mode.