I went through much the same diagnosis on my '86 560SL last year. I actually swapped the IACV from my '85 380SE, and it made no difference (idle on the 380SE is correct BTW). I bought a replacement control module with the right part number off EBay, noting that the one in my car was not the correct part number, obviously installed by someone else at some point. This did make a difference, and at last time the car was on the road (Oct '08), my idle was perfect on start-up, running high for a minute or less, then settling down nicely to about 750. But, it still seemed to be a tad high after the engine had warmed up to operating temperature, not 'settling down' like it did after a cold start. In the spring, I'll try changing the temperature sender to see if it is sending a false signal to this control module. Perhaps this might be something to look at in your case..I'm not sure which sender to check either..

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1986 560SL
2002 Toyota Camry
1993 Lexus