Re: Someone must know??
have you checked the throttle body? the twinsparks have the wonderful oil breather pipe right before the throttle body and so it can easily become clogged up with crap. this would cause the valve to stick shut or to shut prematurely and kill the engine off.
i think the 156 1.8 uses a cable throttle body so its a LOT easier to check than the electrical ones,
remove the air intake pipe from it and peek into the throttle body, it should be nice and shiny and clean... its most likely full of crap. rather than just rubbing it off get a can of carbon cleaner from your local auto store and spray it onto the crap. leave it for half an hour or so to soak in then wipe off with a clean cloth that wont leave bits of fluff everywhere!
you should be safe to open the valve by hand i thinnk but only if its DEFINETLY the cable operated type, can someone else confirm this please?
if not this then you could try an ECU reset, ie, disconnect battert, turn key to MAR, leave like this for half an hour or so, reconnect battery, fire up, let idle for 15 mins then go for a 'sprinted' drive..
hope you get somewhere and WELCOME to the club!