5000 CSQT high RPM idle

[Jon Spensko]

Clan Audi,
New to the list.  Any ideas will be a great help.  My Avant was running perfect and then out of the blue today started to idle at approx 3,100 RPM.  The cable is loose & throttle body closed.  Turbo boost has been finicky just lately, sometimes boost then not.  Everything external on the engine looks correct.  Thanks in advance for any and all ideas.

Jon Spensko
1988 5000 CSQT Avant 163,000
1982 240 DL Volvo 161,000
1994 Explorer 201,000
1992 100S V6-12V 263,000