Jump to content


iacv (idle air control valve) and fitv (fast idle thermo valve)

- - - - -

  • Please log in to reply
2 replies to this topic



    CivicLife Regular

  • Long Term Contributor
  • PipPipPipPipPip
  • 2,120 posts
  • Location:Isle Of Wight
  • Car:CW 96 Spec :D
Seen alot of people recently asking about this. The information is readily available for those who aren't to lazy to search.

Copied from honda-tech.com

I'm tired of seeing everyone ask the same question so here's a general list of things to do to troubleshoot your idle, focusing mainly on servicing the "FITV" (Fast Idle Thermo Valve). Also, if you have a bad thermostat this is the time to install a new one as you need the car to be able to reach normal operating temperature. EDIT: I forgot to mention to also make sure your valves are adjusted to spec as that could also aid in poor idling.

If your idle is stable but either too high or low then you need to adjust it with the idle screw, but don't just turn the screw blindly! The correct way to do it is by letting your car warm up then, while the engine is running, disconnect the IACV (Idle Air Control Valve) electrical plug behind the intake manifold, and adjust the idle screw to 800rpm. After doing that turn your car off, reconnect the IACV plug, then disconnect the battery for a couple of minutes to reset the ECU because you will have a CEL, doing this will get rid of that CEL. Connect the battery and your Idle should be at its normal range - 800 +/- 50 rpm

Most of the time, erratic Idle is caused by a disturbance in the vacuum system, the engine will continuously try to compensate for the loss or gain of air coming into the intake. When you start your car and the engine idles, air bypasses the throttle plate through a couple of holes, one from the FITV and the other from the IACV. The purpose of the FITV is to let extra air in when the engine is cold to help it idle and retain the proper A/F ratio. After the engine is at normal operating temperature, coolant flowing through a thermostat in the FITV heats up a substance inside it which pushes a little plunger that closes the valve that's letting air through on the other side, at that time the IACV will control the idle. The main difference between both of these systems is that the FITV is mechanically controlled and the IACV is computer controlled.

So the first thing you should look for is any apparent leaks from vacuum hoses, bad seals, improperly tightened mating surfaces on the TB (throttle body), IM (intake manifold), etc. If everything checks out move on to the IACV, unbolt the 2 12mm bolts holding it in place then separate it from the IM. It should look like this:

Posted Image

Note the two holes in it; the one you are mostly concerned with is the hole with the screen on it. Make sure it is not clogged or otherwise obstructed by debris. If it is you can clean it up with brake cleaner. Bolt it back onto the IM and reconnect any hoses or the electrical plug you may have taken off of it.

Now we will move on to servicing the FITV. You don't want to keep spending money on your 17+ year old Honda especially since you're thing only one in your family who likes the car so here's how to check and service it so that you don't have to go buy a FITV

1. Separate your intake tube from the TB and look inside, you will see 2 holes. The top goes to the IACV and the bottom goes to the FITV.

Posted Image

2. Start your car and let it warm up to normal operating temperature (fan comes on), then plug the FITV hole, there should be ZERO to VERY MINIMAL suction. If there is suction after warm up then there is something wrong with the FIT valve, turn the car off and let it cool down.

Posted Image

3. This is where the manuals tell you to change the FIT valve with a new one, but there are actually a couple of things you can do to restore your old one. First things first, this is what the FITV looks like, it's attached to the underside of the TB or in some models it will be attached on the manifold right under the TB and it may have 2 coolant hoses, mine had one on the FITV and one going to the IACV from the TB (channeled through the FITV):

Posted Image

4. Disconnect any coolant hoses, vacuum lines, and electrical connectors that may be in the way of the back of the FITV (make sure you mark them so you know where to reconnect them). Now look at the back of the FIT valve, there is a flat plate held down by 2 screws, you'll be removing this plate. Due to the limited space/visibility I used a mirror and an elbowed screwdriver to take it off, you can also use an 8mm socket:

Posted Image

Inside is the end portion of the spring loaded valve, held down by a white plastic piece with 2 slots on either side:

Posted Image

5. This piece is threaded like a screw and sometimes it will unscrew over time, creating too much slack on the spring of the valve and therefore causing a vacuum leak. Screw it back in with any tool that fits the slots. Screw it in tight but don't overdo it.

Posted Image

6. Replace the plate and reconnect everything you had taken off.

7. Repeat the procedure for checking suction at the FITV hole on the TB [STEP 2]

VSM B16 EJ9 build 







    cock lover

  • Established Poster
  • PipPipPip
  • 283 posts
gotta say I did the IACV on my integra, seemed alot better and didnt rev so high when idling :) WELL WORTH doing IMHO




  • Long Term Contributor
  • PipPipPipPip
  • 834 posts
  • Location:Manchester
  • Car:EK3
Good write up, need to do this!

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users