STi stuck in limp mode....help?
 

So I believe my car (08 STi) is stuck in limp mode. The battery was going bad so I changed it (and possibly overboosted it trying to get it to start before I did so), and ever since then it has a hard time starting. I have to turn it over multiple times and rev to get it going. It acts normal for a few seconds after it starts, but then it beeps the CEL comes on and my SI drive Sport light begins flashing and doesn't change when I try to change modes. It can be revved to redline, but dies out when the RPMs get low (around 800). I tried resetting the ECU by disconnecting the negative battery cable and pressing the brake for a minute or two, but when I start it back up the same thing happens. Any ideas? The car was tuned about 6 months ago.