FWIW Last night as I went to leave for work my truck (60,000 miles)was idling at 4000 rpm. I called onstar and got the code" idle circuit module". After examination for a module and not knowing what I was looking for I guessed it was on the throttle body. Walla!!! the engine cover or a gremlin had broken the top wire from the harness to the module I soldered it and am back to normal.
I hope this helps someone else who may encounter this problem