Have this car in with erratic idle, lack of throttle response hesitating and misfiring at low speed and throttle opening. Car runs fine under hard load. There are no codes stored , CTS is showing 140 deg , changed this still same but idle has stabilised. If i disconnect it defaults to 87 deg. I suspect an ecu fault. When you open the throttle the ignition timing is showing -2 to -10 deg before advancing at which point the engine revs cleanly.
Has anyone used Ecu testing.com ? Or has anyone had a similar fault and can suggest anything.