Did the cylinder that misfired have a fouled plug. If it was oil fouled, you may have a leaking valve guide seal. If the plug looks gas fouled, you could have a bad coil, wire/boot, or injector. The ac puts a load on the motor, so at low low rpm, a weak spark will misfire. If you get a misfire code on the same cylinder as before, check the plug, and coil, wire/boot, and injector for that cylinder. The turn signal should not be on when you start the car, unless someone turned it on. Normally, the turn signal being on should not cause a misfire, unless it's system is shorted out, and creating electrical interference with the electrical system. Good luck.