I had almost identical symptoms until yesterday – rough start that only really happened in the mornings, lots of revving to get it warmed up, and it would definitely stumble at the first 3-4 stop signs on my way to the highway. After that it would run like a champ. Gas mileage wasn't severely affected, and it didn't throw codes.

I went through Bentley's section on LH System Troubleshooting (241-4) and in order it says to check Intake Air Supply, Fuel Supply, Throttle Body Deposits, Electrical, and Ignition Spark. I ran through the list and ended at the throttle body. It was filthy. Following the directions in the FAQ here on Brickboard, I gave that little bastard the cleaning of it's lifetime. In fact, judging by how dirty it was it likely was the first time it's been cleaned. I placed it back on the car, and crossed my fingers.

Never have I done one thing to my car that's made so much of a difference. It's so smooth. And when you figure how much it cost – $6 bucks for throttle body cleaner, a toothbrush, and an hour of my time – the outcome is amazing.

It might not be your entire problem, but for the amount of investment needed it may not be a bad place to start.

Hope it helps, and keep us updated.