I hope this isn't too late for you, and you probably have this fixed by now, but I'll offer anyhow.
I had this same thing happen to me. It started out that way and then quickly worsened. It got to the point to where I had to keep steady gas to keep the car running. Took it in and it was the IAC motor. Problems with Idle Air Control. The dealership tried to tell me it was my pump, so look out for this type of thing. Ended up costing about $500. Hope this helps!!
