my car is 90 crx si, with dohc zc motor, has been running really good lately, but out of nowhere today, it started having a fluctuating idle, going up and down from 800rpm to 1500rpm and back to 800rpm....,

it started after i just started up my car after doing some work to it at a car wash stall, and was sitting there for a couple mins with the fan blower on (no a/c), to cool off a little, and then noticed the idle started doing that??, and i did'nt mess with anything in the engine bay that would change anything?, i was working on putting the interior back together and stuff.

can anybody give me some ideas on things to check? or what could cause this to suddenly start happening?

i read around search, and mostly said either vacuum leaks or dirty eacv,

a couple months ago i removed my eacv and cleaned the hell out of it and the gasket was still good, but i made it even better by coating the gasket with black rtv silicone gasket maker and let dry and then put it back together, so i know its not a dirty eacv.

the vac hoses were all good last time i checked too, cause i had to get a couple new ones when cleaning out eacv, i also cleaned out my throttle body and adjusted the throttle cable and adjusted my idle speed by the book and afterwards got it where it was idling perfectly, and it has been ever since (UNTIL NOW!),

i'm going to check the ecu for codes, check coolant level, inspect vacuum hoses and try resetting the ecu by pulling fuse, and see if any of that does anything.

 

You have a vaccum leak, Coolant , iacv problem. You can rule out the iacv by taking the intake hose off and blocking off the hole that is right before the butterfly in the intake manifold. You'll see it . if it settles down when you plug it up you know where to start.

 

Clean Iacv, FITV, or you may have got water in the spark plugs. Might as well check.

 

thanks for the replies for things to check, but its not doing it anymore ?,

i guess it was a one time thing, it seems as though it did that up/down idle thing only after i started car after i was done at the car wash stall, and did it on the way back home,

but later i drove car around neighborhood, stopping at several stoplights, and it was back to normal ???, not doing any of the up&down idle ???, not sure why it would do it that one time?, at least its not a problem i have to worry about.

 

If it happens again maybe there's a bubble in the coolant that will cause bouncy idle for some reason but anytime I mess with the coolant in my car I bleed it too its really easy with the bleed valve by exhaust manifold just crack it open while running

 

Like I said, you probably ended up with water in somewhere it shouldn't be, and it probably dried up. Hope the issue doesn't come back

 

actually back a couple months ago i also bled the air out of the cooling system, during the same time i also cleaned the EACV, cleaned TB, adjusted throttle cable , cleaned air intake and adjusted the idle, so thats why i could'nt believe i started to have a weird idle problem ?, cause after doing the stuff above, i thought i had it covered, as far as idle related stuff.