idle problem

i have a 1990 honda accord, just replaced my water pump and my timing belts also flushed the entire cooling system, the engine will sit and idle high then low...high then low..real quick, but once you put it into gear it smooths out, driving the car is fine, its just at idle when it seems to rev up then back down, anyone have any idea where i should start to diagnose this thing.


note:the engine reved up and down even before the pump and belts change

Either replace or clean the idle air control valve. Its on the front of the intake manifold. Ive heard others say it can be the EGR to but mine was the IACV.