got a 1990 honda accord, just replaced my water pump and my timing belts also flushed the entire cooling system..anyways, 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 rapidly, 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

 

do you use the AC alot? Because everytime the condensor kicks in the engine has to rev a little higher.

 

Did the car do this before the work was done? Did you do the work yourself or did someone else do it? If someone else did and the car didn't do it before take it back to them to fix. If the car didn't do it before and you did the work yourself; check the timing. There are sensors that deal with the idle and what not, but knowing if the idle problem was happening before will help. Idle high, then low might be the computer trying to compensate for it being off the mark. I know this from other vehicles I have owned but are not specefic to the accord so someone else might need to give some info to assist you more.

 

chk for a vacc leak,,,,,,,,,,also make sure that the adjuster screw is not almpst all the way backed out ,,,,,if normal idle is too high the idle will flactuate,,,,,,,,,remove the top cover for the fast idle valve and tighten the inner valve ,, if inner valve is loose idle will flactuate

bleed cooling system, make sure there is not an air bubble and you are low on coolant

 

replaced the idle air control (IAC) good as new

 

thanks for letting us know the fix............

I wish everyone would do that ........