rough idle

Does anyone have suggestions as to what could cause a rough idle on a 2000 Boxster? It bounces betweem 800 and 1000 RPM. I have changed the Mass Air Flow Sensor. I have had Porsche reprogram the computer. I have changed the oil filler hose and it still has a bad idle...I have also had Porsche scan the system and they said that it seem to loose a touch of fuel at idle, yet they can't locate the problem....Please Help...