I ran "smog test NOX" by the wikipedia, yes it's snowing here and I'm bored stiff. Anyway there is a wealth of info there.
http://en.wikipedia.org/wiki/Automobile_emissions_control
Was that the emissions tech that told you to retard the timing? I may be speaking knowing nothing (no doubt true) but more info should help this. Does the engine have fuel injection? Doesn't sound like it with the idle speed floating all over the place. If it does have fuel injection then this is where I'd begin, no doubt the two symptoms are related.
Brian Rodgers

Brian Rodgers
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1989 Isuzu Pup gasser
2-86 Isuzu Trooper turbo diesels (1 good 1 bad)
Many gallons of biodiesel since 2005