i have the same car with the same problem .i had a diagnostic done and it said it was my electric throttle peddle was at fault .i had that changed but still the same result .the garage said i had to go to a vauxhall dealer so went there had another diagnostic they say i need a new ecu but they dont have one and cant get one . so i got in touch with a firm to see if they could fix an ecu turns out they cant fix vauxhall ecu s.i dont know what to do now except find and buy a new ecu and have it fitted at a cost of £600 and even then im not sure if that will fix it .
john
February 2010