(UPDATE/FIX) 2000 Civic SiR low, rough idle

Original post:
Hey, I was wondering if anyone could shed some light on what would be causing this: 2000 civic sir with 120000km on it.
Intermittently idles low, like 500rpm, with a rough feel to it. If I tap the gas rpms jump then just drop right back down to 500rpm or so (the line just above the very bottom line on the tach). It slowly comes back up to 800rpm or so but if you tap the pedal it drops right back down again. It can do it once or 4 to 5 times in a row this way. Oil changes done regularly and according to the user manual the plugs don't need to be done until 160000km.
After trying a bunch of things (thanks TeGGer), including vac leak tests, base idle adjustment, new IACV it turns out that my throttle body had a build up of carbon all along where the butterfly flapper comes in contact with the throttle body. Cleaned it with some throttle body cleaner and voila my idle is good now!
Although the throttle still feels like it is sticking slightly, but it idles good.
thanks for all the advice
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