In the last month or two my car has been getting this rough idle when i start it up after driving it somewhat hard. The rpm's fluctuate from 1.5 to almost 0 for a good 20 seconds or so before it goes back to normal. The car wont do this if i really baby her on the gas, only when i open it up or go through stop and go traffic in town will it do this. Any ideas what it could be? Something like a fuel pressure regulator, or as simple as a vacuum lines disconnected?