Ok. New update. Fuel pump became noisy, so placed new uprated one.
One injector had bad spray pattern, so place 4 brand new original Bosch ones.
Replace sparkplugs with iridium ones. The old plug of cyl. 1 looked like running lean.
Placed a lambda sensor in the exhaust and with an AFR meter, it shows rich on full throttle. So that should be OK.
Powerwise all is fine now, but still starting on 2 or 3 cylinders when cold. Disconnected cold start injector, but still starting on 2/3 cyl. Takes longer to start then, as expected. Also still holds back at half throttle on 3200 to 4000rpm. Full throttle is fine.
I found out that the remaining fuel pressure after the pump is still there after 2 weeks, but when I exchanged tje injectors, there was none remaining fuel pressure on any of the 4.
Broken regulator or distrubuter?