Hello and Welcome!
VERY nice car!!!
Most likely sensor issue.
MEASURE the following and compare to FSM specs:
- IAT sensor
- ECT sensor, combined with above, DME uses to determines cold-start enrichment +20-30% fuel
- crank & cam sensors, measure waveforms with oscilloscope and compare to FSM
Without measuring, problem part will NOT be found and you will be replacing A LOT of perfectly working parts with brand-new perfectly-working parts and NOTHING will change. You'll end up replacing 100s of parts and spend 1000s of Euros before you accidentally and luckily replace actual problem part without actually ever diagnosing problem.