I didn't see what you wrote on the problem, but if there is an unmetered air leak then the idle will be high. That idol is where it would be subject to the highest vacuum.
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Not knowing exactly what kind of car it is and what kind of system it is, another source the problems could be two other things, bad IAC valve(Idle air control) Or a stuck PCV valve (positive crankcase ventilation)
But since it was a used gasket I would say the likelihood it is the old throttle body gasket that is leaking