On three widely-spaced occasions, I had trouble starting my 05 V8 SRX. It would fire, then run very roughly, sometimes quitting and having to be restarted. On one occasion, it started in my garage, rumbled and shook, emitted a huge cloud of smoke, and then ran smoothly. In each case, it eventually smoothed out with no further problem. One time I had to restart it a dozen or so times, but fortunately the battery held out and it took off. It has nearly 70k miles and has never been tuned up. Any ideas? Injectors? Ignition????