I have a 01 S80 non Turbo, auto trans, that does this on cold days or warmer days after not being used for several days. Noisy revs and almost dies from near stall to 3000 RPM. I don't know if it helps straighten it out, but I always feather the accelerator pedal quickly and it calms down. I have never let it run on its own for fear that it might go higher than 3000.
I have never received error messages and I am in a very small rural town where the only repair shop does not have the capability of scanning. Other than that it runs flawlessly.
Any suggestions as where to begin troubleshooting?
Any questions for me?