[ploo]

I had a similar problem and was convinced it was my idle control valve. On cold start, my car would nearly stall and idle very roughly until I warmed the cats up. However, the dealership found no ECU faults and suggested it might be a batch of bad gas, especially as additive formulations do change around this time of year for the winter season.

Sure enough, the problem went away with gas from a different station (Chevron). Who knew the solution could be so simple?

Good luck!