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
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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.

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thank you i will try that and update status
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normshonda wrote:

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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'
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'Curly Q. Links' wrote:

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.
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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
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normshonda wrote:

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
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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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normshonda wrote:

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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'
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normshonda wrote:

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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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