I feel the need to share this story after I went through such a headache.

I brought my car (97 Honda Civic EX) to a shop to get the clutch replaced. When I got it back the mechanic told me that when he test drove my car after the installation, that I have a widly varying idle. I had never had a problem with my idle before this point but I gave the guy the benefit of the doubt and assumed my valve was old and needed cleaning.

What my idle was doing:
It would bounce between 1 or 1.5 to 2 or 2.5. If it ever settled it would be around 1.5 or 2. I could tell the sensors were working because every now and again they would try and compensate for the crazy idle and regulate it around 1.7. When this happened it would cause my car to buck when I accelerated below that RPM.

So, the next weekend I took my IACV off and cleaned everything out of it. It wasn't really all that dirty (but I didn't know the different at the time). I replaced it and then went for a test drive. At first it seemed it had worked. My idle was lower and wasn't varying but it wasn't where it used to be. I drove it like that for the next week hoping it would get better. It didn't. So I tried cleaning it the next weekend. This time I reset the sensors too, hoping they just had a quirk in them. I also tried cleaning the throttle body this time. Again once I replaced everything and went for a test drive, things seemed to be getting better. But then they would only get worse as the week progressed.

I finally buckled and bought a replacement IACV. I got a used one from an auction on Ebay. When I recieved it, it looked dirtier than my current one. But I gave it a try anyways. I switched IACV's and went for a test drive. Again, seemed like it had worked but again it only got worse as time progressed. I also noticed that there was a screw to change the idle on the IACV and I tried adjusting it there. But the adjustment took a special 5 sided adjusting tool. Which no one has ever heard of. So that didn't work.

I was about ready to give up on my car when my dad was looking at it and noticed there was a hose that seemed to be disconnected. It ran to the cruise control (btw my cruise had stopped worked for some reason...I thought I had blown a fuse). After about 20 minutes of trying to find where this hose went, we found a hook up right bellow the IACV on the air chamber. We hooked it back up and started my car....the crazy idle was gone. A few angry curses ensued.

So, if you have a crazy idle and nothing seems to be working, check to make sure all your vacuum hoses are connected. Even if the cars computer is telling you it's the IAC system. Oh and never trust a mechanic when he says you have a problem that never occured before he messed with your car.[:@]

 

Well, glad to hear you got it all figured out.


The vac leak is where I would have started my search, keep it simple and look for things like that before you just start throwing new parts at it.

 

This is funny because I have the same idle problem when my cruise is plugged in. When I unplug the cruise control vacuum hose, the car idles fine.

Any ideas?

It is a 96 EX.

 

hhmmm, thats odd. With the cruise hose just hanging (open) you dont surge or anything

 

Yes that is correct. There may be a slight surge but not very noticeable at all.

But as soon as I connect the cruise hose and start it up, it idles very rough and stalls when slowing down for turns or what not.

I should probably give a little more info on this car.

I purchased it about 3 weeks ago. The engine in it was replaced with a D16Y7 by previous owner. The car is a little rough (project car ) but the engine seems to run fine as long as I leave the cruise hose disconnected.

Also there is what appears to be a vacuum hose coming from the top left of the valve cover that isn't connected to anything. And I can't see any place in reach that it will connect to.

 

There is a hose that goes into the head near the intake mani. and the valve cover on my z6 and it was cracked and broken. It would spray out coolant everywhere. My idle was weird like that until I fixed the hose. Now its fine and my car doesnt overheat because of lack of coolant!

 

thewayne, you have pics of these hoses?

Sounds to me like whoever installed the motor forgot to hook something up, then compensated by "fixing" something else. ie, idle was surging, so they did whatever they could to make it stop (unplugged cruise). So once the lines are run properly again, it surges due to over compensation and/or not being fixed properly.

 

Not to sound stupid but whats a IACV because I have this exact problem with my car.

 

Idle Air Control Valve

 

I will put up some pictures when I get home from work.