My bone-stock (except for stereo system) 2005 conv started to malfunction at idle (high, low and engine shut off). Few days later entered failsafe mode that cleared itself after restart. Now it does that more often and my SCT gives me codes p0521 and p0321. After I clear them with the tuner the reappear in awhile. No custom tunes loaded, just stock. High summer temp a factor? Any ideas what to do? No dealer available...