Sorry to say yes its true everything is controlled by the engine management system so is not adjustable saying that it could be a sensor issue causing it to idle slower than normal.I am sure they could check it out but if yours still not happy take it to another Vauxhall dealer for a second opinion
Hi, when you say idle is low, how low is it? When cold it should idle around 1100 rpm then drop to around 850 when warmed up. I would defo get a second opinion and ask for any fault codes. Sounds like a sensor somewhere.