This may help..
Porsche updated the MAF some time around 2000-2001. The new part number is 986 606 125 01; the old part number was 986 606 124 XX. To use the updated MAF in an older car, the software has to be reflashed, and there is a TSB for this.
I had the older MAF in my 2000 BoxS and it went bad, so I decided to update with the newer unit. A local independent BMW/Porsche shop said they could do the re-flash, so I installed the new 125 MAF myself and took the car to them. $400 later I drove away and the car seemed fine, no CEL, ran great, and improved MPG's to boot. About a year later I put the car on a dyno and discovered that the car was actually running a bit lean. I figured it was the intake and headers that I had added. Maybe I had a vacuum leak. The hunt began...
I could not sort out this vacuum leak to save my life. Using my Durametric, I tested the O2 sensor values and it always showed the car running lean.
I got my hands on an old 124 MAF that I knew was good and tried that... Presto! Durametric showed that the fuel mix was right where it belonged.
Whatever the indy shop did, it did not work. However, the car ran with the 125 MAF on the lean side, but not so out of spec to trigger the CEL.
I've got a feeling that your rough idle may be similar to my issue.