my 98 honda civic idles up and down when warm

i have a 1998 honda civic when it gets to normal temp it idles up and down
have had it to garage they cleaned iac sensor reset ecu and couldnt figure
it out it never stalls out and runs fine when driving just when idiling it
goes up and down it was sitting at guys house for 6 months while he put
ground effects kit on it whe ni took it there it didnt have problem now it
does if you have any idea what would do this please let me know thank you

 

As a first step, read your owner's manual's directions on topping off the
coolant system and purging it of air.

Coolant cools the IAC valve on most or all Hondas. Low coolant levels or an
air bubble will cause the idle to act up. Had some of your symptoms on my 91
Civic last year. Took apart the EAC valve (same as the IAC valve) and found
its coolant line had a big air pocket in it. Sure enough, a proper air purge
fixed it right up.

During the purge steps, getting the radiator fan to come on twice may take
40 minutes or more of idling. Have a magazine.

 

thank you i will try that and update status

 

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Another suggestion: Top up the reservoir to MAX in the AM, before
heading to work, and check it again next time engine is cool. It 'sips'
coolant each time engine cools down the first two or three times . . .
Don't use tap water, get Honda premix.

'Curly'

 

bleeding coolant didnt work still going up and down someone told me to put
my finger over hole in throttle body i did that didnt change any thing
does that mean there is a vacuum leak somewhere

 

I ran into a problem on a '90 Accord with a surging idle. After bleeding
the cooling system of air several times, it turned out that the coolant
passages in the EACV were blocked with rust and no amount of bleeding was
going to correct the problem. If the air control valves don't get hot as
the engine is warming up then there could be a blockage somewhere in the
coolant lines.

Eric

 

that doesn't work of there's a leak in the system - it sucks air through
the leak in preference to fluid from the reservoir. that's why it's so
important to check in the rad, not just the reservoir.

 

if you take off air intake and plug hole in manifold is it supossed to idle
up or down i plugged it and idle went down does anybody know what that
means

 

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You're supposed to bleed AIR from the cooling system. You have to be
sure there's enough coolant to the top of the rad and in the reservoir,
and that the system is air tight or it won't be able to draw in coolant
to replace the air that gets displaced.

'Curly'

 

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It means you're going to start blowing (sucking actually) gaskets and
seals because you've plugged the fresh air entry point of the PCV
system. Better leave to oil filler cap off if you want to try that trick
(but it's messy).

'Curly'