The Corrado does have an automatic fuel enrichment setting when cold, where the engine behaves differently to when warm, which if not working right can lead to an eratic idle. What can cause this, unfortunately can me a number of things. I haven't heard a fuel pressure problem only occurring whilst cold (except when you arent holding pressure in the lines which presents itself as a starts second time, everytime symptom usually). As bigpants says it could be the ISV, your MAF, but also there is something in the VR6 which I can't remember the details of which effectively monitors emissions, with
