You have a wiring malfunction somewhere... the question is where. Next time it goes screwy, smack the steering wheel, like on the right or left side like you're trying to push it to the passenger side. Sounds silly, but in my merq after I had the airbags attempt to save me from a deer, the turn signals never really worked right when it was cold. The four ways would work, but the turn signal would flash fast and only one light would blink. You smacked the wheel, and it came back to life, or you left the heater on a little longer on hot, and they would work fine. We figured the problem was the clock spring connection got hit when the air bag went off. I never replaced it because, well, I didn't care. Have your airbags ever been set off? And, do your four ways work when the turn signals don't?