This is most likely the ICV. Quick and dirty test is to pull the plug of the ICV see if there is a difference. If no difference it s probably the ICV. If there is a difference then start with the duty cycle. There are loads of threads on high idles on 560's, I would suggest spending some time going through them alot may have similarities to your issue.

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Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)