I am currently on a ferry moving out of town and i had to kind of rush to get my Civic going.
Before i had a chance to sit down and diagnose, i had to leave so i have a little problem.

My car has the hedman header and a custom 2.25" pipe exhaust and it just got done. My idle is fine when cold but as soon as it starts to heat up, it revs up to 2k and drops down to 1k over and over again. i have 2 CEL's for my secondary O2 sensor (it's not hooked up) and i don't think it would do that to me, cuz it's only to make sure the cat is working (which i don't have either) any ideas on what this could be so that i can have a look at it as soon as i get off the boat?

I've had a busy week and i'm gonna have another one ahead of me so i won't have all the time in the world for diagnosing (i wish i did) any help would be great.

 

Mine's doing something very similar and I've been getting no responses... if you get your car checked out please let me know what the problem is... cause mine is driving me crazy...

 

hook up that second 02 sensor

 

heres what you can try.

take off your Idle Controll Sensor its located in the back of ur intake manifold. there should be 2 bolts and 2 lines and a eletric plug.

clean it nicely also the back of your intake manifold.
*IF THAT DOESNT WORK*

. check your coolant (sometimes the IAC can idle stupidly cuz it thinks its lacking coolant so it gets confused and starts throwing rev's)so you have the get the air bubbles out.bleed it until u have coolant coming out and not air (bleed it by the thermastat)

*IF THAT DOESNT WORK*

Lower your idling by adjusting the idle screw on the intake manifold (this worked for me)

*and lastly of that doesnt doit*

then that means your idle control sensor is going out.... and you have to replace it. (easy install) if u just go to a local honda dealer and buy a new 1

 

Would the secondary O2 sensor really have that effect?
I know it's only for monitoring the functionality of the catalytic convertor, so i figured it was moot considering i no longer have a cat.
which relates to money problems, moreso than wanting that extra hp. Once i start getting a paycheck from my new job (canadian tire!!!! lol)
i will get a magnaflow OBDII cat, but up until than i can't.

also, my primary O2 sensor had to be lengthened obscenely to get it into the hedman O2 bung built into the midpipe.
So it would take a whole lot more to get to one after the cat, once i get one. I recently bled all the air out of my coolant, so the other suggestions i will try.

 

+1!

yes, it could be affecting the idle

 

if so, why does the O2 sensor alter my idle like that? not to say you are wrong, i would just like to understand.

 

The O2 sensors job is to keep a balanced mixture of air and fuel(if the balance can not be found, an irregular idle will occer). When the sensor is not hooked up or not working for some reason the car will end up running rich(so the least engine damage will occer....if it were to run lean, you can severly damage the internals of your engine). It's best to always have your O2 sensors in GREAT working oreder.... you can find them online for pretty cheap.... if you drive your car hard, and or have alot of mods i would recomend replacing the O2 sensor every 10-20 thousand miles.

 

thats for the primary O2 sensor, it's job is to measure the air-fuel ratio, but the secondary O2 sensor is just meant to monitor the condition and effectiveness of the catalytic convertor. I may be so used to Domestic vehicles here, but i know with the integration of OBD-II they have standardized the emmisions system for easy monitoring and servicing (to an extent, there are still some variations)

So my understanding was that it does not effect performance or engine operation, but like i said i could be wrong.

 

my friend has a problem with that in his truck and it was his IACV (Idle Air Control Valve).