High idle - intermittent

I have a Dec 1999 Toyota Camry Conquest with a V6 3L engine (1MZ-FE), automatic, 135,000km. Sometimes (10-20% of the time), the idle sticks
high (900rpm). Most of the time it idles at 700rpm.
This high idle problem happened recently (3 weeks ago). It is not related to AC, engine well warmed up, temperature gauge display normal. Tapping gas padel does not set it back. If the idle is at 700, change from neutral (N) to drive (D) is smooth. If it idles high (900), N to D change gives a forward kick and the idle drops down to 700 (when in D).
When it idles high, transission from first gear to second also gives a forward kick.
Firstly, I have suspected the IAC. After extensive searching of the internet, it looks to me that the IAC problem is more to do with low / unstable idle.
Any relevant suggestions about the possible source of problem or solution would be highly appreciated.
Regards,
Sam Yang snipped-for-privacy@csiro.au
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Just some further information:
My Gregory's service & repair manual (No 276) has a way to test the IAC valve. It says if I bridge (connect) E1 & TC of the check connector (under the bonnet), the idle will increases to 1000 for 5 seconds then returns to normal. When my car is idle at 900 rpm, bridging E1 & TC has no effect to the engine. When my car is idle at 700rpm, bridging E1 & TC will increase the idle to 900rpm, then it drops back to 700. In either case, bridging E1 & TC will set off a ABS light on the dash board.
At this stage, I am suspecting a sticking IAC valve (stick open). Does this make sense? I am going to clean it using a carby cleaner. Is the carby cleaner without silicon is safe for sensors?
Regards,
Sam Yang
snipped-for-privacy@csiro.au (Sam Yang) wrote in message
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snipped-for-privacy@csiro.au (Sam Yang) wrote in message

Not familiar with your particular engine, but generally speaking, the carb cleaner container needs to specifically state "safe for emission controls" or something similar -- if not explicitly mentioned -- find another brand. Also, thry spraying the carb cleaner into the air inlet for the IAC valve with the engine idling, keeping it running by moving the butterfly valve at the throttle body to work the cleaner through the valve. When cleaning the IAC valve with the engine off, I have found the idling problems return much sooner.
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