Looks like this little Scooter is on its way to an economic write off...
Sure, sad to think so, but...
Too many parts involved which might be the cause.
The only way is to bring it to the dealer, give him 1 or 2 more chances to fix it under warranty and then give the scooter back, step back from contract, ask for a refund. Should be possible, as this is a major fault/issue, nothing minor stuff.
Even a good garage and a good mechanic will probably need hours or days to search and investigate. Who is going to pay for all these coming labour costs?
Nowadays thats in nobody´s interest. Neither in dealer´s nor Kymco´s. And for sure not in Stig´s.
A diagnostic tool is an absolute must have to at least check the other parameters of the throttle body, the Sensors and the ECU.
Your dealer´s Service Dep. MUST have or at least organize such a diagnostic tool and use it. Kymco should and must help.
Probably you better now get in contact with the Kymco Main Importer USA and ask them what to do and how to continue.
Continuing by guessing and trying and replacing this or that on your own, or asking some street guys every now and then doesn´t make any sense any longer I think.