Did you know that it takes about 30% more E85 volume than gasoline to keep the ratio stoich? It must be running lean as hell right now, and your saving grace is that it has 105 octane.
You really can't just dump E85 in the tank and expect it to run right. You can expect to see a check engine light about the next time you drive it, because the computer will be confused that the readings on the O2 sensors don't match with what it expects.
Your computer really can't compensate for the extra fuel volume required for E85. Most cars can compensate for up to about 40-60% ethanol before throwing a check engine light, but not 85%. If you really put in 12-14 gallons, I'm surprised you don't have a lean miss or lean surge. I was running E30 in the 97GT without a problem, but that's a long way from E85.
Were you hoping to save money? Your mileage will go down, resulting in basically the same cost per mile.
In the very minimum, you need to run injectors that are ~30% larger which will effectivly trick the computer into thinking you are running gasoline. This is what I did on the 88 2.3, but of course you can't switch between E85 and gasoline without retuning.
In conclusion, sell your stang because you don't have a clue what you are doing.