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Yes, it could be something like a temp sensor, but in that case you'll typically see a major drift in idle as the engine warms up. Check the 700/900 FAQ here for more information on that problem area.
The idle air control valve is always a suspect when it comes to idle problems, but the prime symptom is usually a fluctuating, erratic or warm/cold sticky idle between 600-1300 rpm. Based on your symptoms and especially as you've done a parts swap with a known good IAC valve then you've pretty much eliminated that thought.
For a high idle in the 1200-2000 rpm range or a widely floating idle it's more likely the idle is simply out of control, i.e. the ECU doesn't even know it's supposed to be controlling idle or is totally unable to control the idle. Typically this means the ECU simply isn't seeing the throttle switch close when you take your foot off the pedal. This is often due to grunge in the throttle throat preventing the plate from fully closing or badly misadjusted throttle body linkage/switch or a loose/open connector or possibly a faulty/sticky switch -in that order of likelihood. I'd start by doing a complete throttle body cleaning and readjustment before looking elsewhere. Look in the 700/900 FAQ here for tips.
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Dave -940's, prev 740/240/140/120 You'd think I'd have learned by now
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