G'day guys, Today I had an Ex-force 2.25 catback system fitted to my VF SV6 and now the car idles rough when in drive. Under load no issues at all. Gets worse with the Aircon on. I spoke to Holden and they said the new exhaust might need to be de-stressed. Anyone ever heard of this or have any idea what could be the cause ? Car idled perfect before exhaust was fitted. I took it back to the exhaust place and they checked the sensors and said they were fine. Any help would be appreciated.