Hi guys. I have had an engine ecu update this morning to stage 1. when testing it afterwards it drove fine for a few mile without putting my foot down. I then accelerated to test the update and noticed an obvious difference in increased performance. after letting my foot off the power I then had no power again afterwards when trying to accelerate. you can feel the engine hesitating as if it was juddering and lacking power. also had an eggy smell from the exhaust. any ideas as to what could cause this?