[theflash32]

OK, as advised, I changed the accumulator and everything is fine now Thank you for all the kind support.
lesson learned, F1 ACUUMULATOR NEEDS TO BE CHANGED EVERY 10 YEARS, regardless of mileage, the rubber membrane inside just disintegrates, ait trapped inside helps retain some pressure reservoir function, but the fluid aerated and pressure erratic, all kinds of weird shifting problems happen.

Glad you took my advice and it worked out

Did you buy from the place i mentioned ?

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[theflash32]

Now that it is working fine
.you should post some graphs and cycle times (on and off ) so other will have a reference of a "good" system

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[murat]

Glad you took my advice and it worked out

Did you buy from the place i mentioned ?

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I ordered a magnetti marelli from Amazon, it took a while to arrive but genuine article.

 

[murat]

Now that it is working fine
.you should post some graphs and cycle times (on and off ) so other will have a reference of a "good" system

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below are pressure (bar) versus time (sec) graphs with good and bad accumulator. I am surprised that the system gets to a higher pressure with the bad accumulator.
the pump motor turns on at the same low press. setting, but with bad accumulator it appears that pressure overshoots due to lack of pressure buffer. I think pressure loss is slightly more rapid at idle even with good accumulator but not significant. I didn't take good data to compare idle vs ignition on with new accumulator.

 

[StefVan]

Interesting, thanks for sharing, it looks like you've fixed the first step of your issue as the pressure is now holding up longer (about 5 min?).
Is the "Good accumulator" graph with ignition on only or engine idling, warm or cold?