just to update - there was a leak from the high pressure pipe going to the pump, and also from the regulator, so it got the high pressure pump kept taking more and more power from the engine.
https://www.youtube.com/watch?v=soxdfjE6BN4
i uploaded a video where i rebuild the regulator, have fun watch.

Hi. My name is Eli from Israel. I have a 89 BX GTi with 1.6L XU5J (like the 205 gti) My Idle is preety rough. I know the rpm should be around 850-950 but if I asjust it to be just below 1100 the rpm drops each time the pump engaging to around 500. So i adjist the rpm to be around 1200 which is high....