accord idle problems
 

My 1990 accord 2.2l lx 5 spd manual 141,100 miles. the vehicle idles low (300-500) after warm up, when coasting in neutral downhill the idle bumps up to approx 1600 and stays there, when you come to a stop, the idle returns to 300-500.??
is there a way to adjust the idle (iacv/eacv) \??
if not how difficult is it to replace? thanks :confused: