We have a 96 civic with the D16Y7 / manual transmission and are having troubles with the car's idle, especially in the heat. At any ambient temp it will often start right up, and then nearly stall out, dropping to just a few hundred rpms. If you get on the gas it will recover. When it gets warmer outside, it adds another symptom. The rpms will actually surge up to as much as 3000 rpm with no throttle input. It does this in gear as well. If you put it in first it will drive itself up to 3000 rpm. It does this only intermittently though.

Any ideas?

I'm thinking Idle Air Control Valve, but I don't want to jump into it unless you guys agree.

One other note: I have a code reader and there are no DTCs stored in the computer.

Sorry for the B in the title

 

well first thing i would do is park the front end of the car at a up incline and with the car cooled down remove the radiator cap fill it up then leave the cap off and start up the car and let it idle for awhile and keep toping off the radiator fluid if it gets sucked down alittle then after ruffly 10mins or so after the temp has been warm for awhile then again top off the fluid and pop the cap back on.

hopefully that will bleed the system good and ya wont have any bubbles in the system that typicaly throws the idle outta wack.... and if not then clean the IAC and try again.
those are typicaly the 2 problems off the odd idle.

 

i totally agree with addiction2bass bleed the radiator and clean the IACV, if the problem persists try and find a used IACV and see if that fixes the problem. i have a y7 and i ended up having to swap the IACV

 

that's weird that it would do it in gear...
is your throttle cable too tight?

 

How would a tight throttle cable cause an increase in RPM with no throttle input?

Can I use any old premix 50/50 (I happen to have some at home from a while ago) or do I need Honda fluid?

 

Thanks everyone btw!

 

if the throttle cable is overtightened, the butterfly in the throttle body will remain opened a little bit at all times. how far it stays open depends on how overtightened the cable is.
basically, having an overtightened throttle cable is like having your foot on the gas pedal a little bit at all times.

some people say use honda fluid for everything but i'm using some Prestone 50/50 premix antifreeze and it works great.

 

well pull off your radiator cap and look at the fluid... if its green go ahead with typical stuff... if its blue then IMO go with honda fluid. its premixed. thats what i put back in my 96dx i just got.
as to the throttle cable not sure... with the motor off move the cable on the throttle body and see if its really tight or if has a tiny bit of play. usualy they dont tighten up so i wouldnt think that would be it...

 

The idle does drop to normal levels regularly, so I don't think it's an overly tightened throttle cable. I've also played with the throttle at the throttle body and don't really remember a pretension on the cable, but I'll check for it anyway.

I also learned that Honda fluid = blue. Something new! Thanks for that. I'll check it all out tomorrow.

 

Also a vacuum leak anywhere will cause the idle speed to increase.

Check your Fast Idle Valve. This is a thermostatic valve in the bottom of the throttle body, which should be active only in cold weather. If you take the intake pipe off you can block the inlet to that valve with your finger and see if idle decreases.