Do you have erratic, loping, searching, bouncing, or however you'd like to call it, idle problems? Here's a general
list of things to do to troubleshoot your idle, focusing mainly on servicing the "FITV
" (Fast Idle Thermo Valve). This tutorial assumes you have no CEL (check engine light) codes, you must take care of those first (chances are that's part of the idle problem). 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...
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 (wait until the fan comes on) then, while the engine is running, disconnect the IACV (Idle Air Control Valve) electrical plug behind the intake manifold, then 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. Recconect the battery and your Idle should be at its normal range (usually around 650rpm). Idle control screw location: refer to post #76 (http://www.superhonda.com/forum/3991603-post76.html
Most of the time, erratic Idle is caused by a disturbance in the vacuum system, the engine will continiously try to compensate for the gain and loss of extra 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/attain the right A/F ratio; after the engine is at normal operating temperature, hot 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 (that's why it's connected to the harness).
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:
Note the 2 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 carb/intake cleaner. Bolt it back onto the IM and reconnect any hoses or the electrical plug you may have taken off of it.
EDIT: I forgot to mention to also make sure your valves are adjusted to spec. Yes, valve lash (improperly adjusted intake/exhaust valves) can cause erratic idle.
Now we will move on to servicing the FITV. Most of the manuals you read tell you that if you suspect the FITV to be the culprit of your bad idle, you should throw it away and buy a new one... I'll show you how to check and service it so that you don't have to go and spend money unnecessarily on a new FIT valve.
Separate your intake tube from the TB and look inside, you will see 2 holes... the picture below is self explanatory:
Now start your car and let it warm up to normal operating temperature (fan comes on), then put your finger in 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.
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 "fix" it. 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 has one on the FITV and one going to the IACV from the TB (channeled through the FITV):
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:
This is the FITV plate in an exploded view image on a GSR manifold:
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:
Inside is the end portion of the springloaded valve, held down by a white plastic piece with 2 slots on either side:
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 (I used the flathead side of my elbowed screwdriver, turning it clockwise):
Replace the plate and reconnect everything you had taken off.
Repeat the procedure for checking suction at the FITV hole on the TB (Steps 1-3). If there is still a lot of vacuum in the FITV hole, go to "Part II" below.