Hello Again, To try and answer some of your Q's I will start with the car in my ownership - the problems I had were many and I never solved them all. In a nutshell, the exhaust had been butchered, the underside of the car was showing signs of corrosion, the suspension turretts needed welding repairs, it would run lovely one day in five and after changing every single sensor, stripping the distributer,re-fitting the exhaust, re-making the induction system and goodness knows what else I gave up!!
The car as built was very special with blueprinted engine, Abarth style high lift cams,modified ECU, special induction and exhaust and uprated suspension.I always suspected the ECU but was never able to get to the bottom of it. At the time I had my Black Sedici ( in fact at one point I had 2 others!!)and decided "enough is enough" as I just could'nt throw any more money and time at it.
In the end I traded it in to a specialist trader, bought a Punto Sporting and concentrated on my Black 5 door as the "hobby car", If I hadn't already got this car which is mint - I would have kept the red car. Anyway after 1 or 2 more owners Roger aquired the car and correctly identified the Ecu problem ( which I knew about) and also over fuelling. Also by then other problems had manifested themselves and I believe he had a replacement head fitted - transferring the cams across - loads of other work done rsulting in the car you now have.I understand the owners after me wreched the car!! Roger effectively acquired a complete "dog" from what he told me at the time.
Phewww......You still with me.
Anyway back to your problem - I would as a matter of course check the wiring to every sensor and also the HT leads just incase its a lead breaking down. If nothing obvious then I would try the K&N approach as I described earlier - it cost very little to have the pipe work made up by a local hose supplier. If the car has the scary cams in it logic tells me it will need to breath both in and out with greater efficiency than an ordinary car.
It might also be worth trying v power petrol or similer just incase it is a case of crap fuel (I don't know how many miles you have done). Failing that I guess its a case of working through everything methodically. Can you describe in more details exactly what happens.....there are others on this forum who may be better placed than me to answer. CHEERS MIKE