1993 Chevrolet Lumina 93 Chevy Euro 3.1 EFI V-6

I left the ignition on overnight by accident, next morning battery was dead, charged battery, car starts, idles very fast and engine surges until warmed up then it won't idle unless you keep your foot on brake and gas. I ran a scan several times by turning ignition on and off 3 times and engine light just repeats 12 over and over also bought a scan tool and same results. What might I have overheated by leaving ignition on without it running or what do you thihk my problem is? Thank You