Does sound alot more like the IAC is not sweeping properly (due to gummed up movement or electrical falure)... As for the codes only the first code and possibly the second are worth the time of checking out... Most of the time its the first code the rest are just a result of the real problem... Also with that old of a car you might just have a intermitant connection problem with is sometimes very hard to find... Without the engine running take the time to go to each plug and disconnect it, inspect for corrosion and reconnect them... You might even cure your problem...?
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