Is this idle characteristic a problem?

[Shinare]

I drive to and from work on the highway for about 20 minutes every day. Most of the time its 50-60 MPH depending on the traffic. On the way home I cruise for about 5 minutes at 65'ish before taking an off ramp that ends directly at a red light. As in leave highway, foot on brake until the light. I've noticed that when I get stopped at the light after exiting, my car idles weird. It sounds like its idling a tad high maybe, but it sounds OK, but then the idle will drop down so low it almost sounds like the engine catches itself from dieing and when it catches itself it revs up to what I might expect would be normal or a little high. Then it dips down and catches itself. Repeat several times or until the light changes to green. Its like this every day. One day a while back it did actually die on me and I had to restart.

Mechanically I have a completely stock Yaris 3 door hatch back with manual transmission.