Do you mean you have a single cylinder miss, or a rough idle.

If you have a rough idle, this may very well be spark plug related. Did they replace the plugs? The factory calls for, I think, .038 gap on standard, not platinum plugs. Use standard plugs with a .035 gap and there will be a noticable idle quality difference. The platinum plugs have a very thin center electrode that gives a thinner spark.

Good luck,