The only thing I can see in my aftermarket manuals is that it should be half-open at room temp (68 degF, 20 degC) going to fully closed within a few minutes of applying current to the bi-metallic lever or for a fully warmed (hot) engine, so that's what I'd shoot for when checking and adjusting. As long as you can compensate with the air bypass screw, it probably doesn't matter a whole lot if it's fully closed or a hair open on a fully warmed engine.

Further reading suggests the little return spring inside can get week with age. I suppose the bi-metallic lever could also suffer a bit from age. I recall using a drill bit shank as a gauge when adjusting the nut, something like a 1/4" bit at ambient (room) temperature, perhaps someone can confirm that adjustment. Add a bit of grunge or a wear groove in the bi-metallic lever and it could mean you're not getting a nice consistent closure when warm.

If tapping it causes the warm idle to change then I'd attempt a cleaning, like spraying in some penetrating oil or WD-40, rotating the plate to the side so you can work it in, followed by dipping it a number of times in a shallow solvent bath to rinse it clean, keeping the bi-metallic lever end pointed up and mostly out of the fluid, followed by shaking it out and compressed air to dry it.

Once, when worried that someone might have been playing with it ahead of me, I remember forcefully turning the electrical connector to rotate the bi-metallic lever back and forth a bit to make sure the lever was square to the little tab and allowing maximum closure, not that I'm suggesting you do that, just that turning the electrical connector will alter the lever orientation inside and could change behaviour for the worse. I actually pulled an old one apart to see what made it tick and after cleaning and adjustment kept it as a spare. You won't have to pull yours apart, I found a couple of images that may help you.




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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now