• February 20, 2009
• Category: DIY
• Written By: MonopolyMan
• No Comments

A very common problem with Hondas is an oscillating idle, that basically means that your idle revs up and down for no reason. Which can be caused by all of the following. This is a guide I have written to help people fix this problem.
I learned how to do all of this from research off the Internet, I read a lot and taught myself what could be the causes of an oscillating idle and then traced it down to these common things.

The first thing you have to do is check your vacuum routing. On the underside of your hood there should be a vacuum diagram. If there isn’t a diagram under there, there is one in a Helms, Chilton’s, or Haynes manual for your car (If you don’t have one already, it is suggested that you buy one before beginning). Remember, ANY extra air will confuse the ECU. Check for cracked or bad vacuum hoses. If in doubt, just replace the damage hose; they aren’t very expensive. The PCV valve could also be the culprit. Take it out and examine it. If it is cracked it could be causing a vacuum leak. Replace the piece if you aren’t completely sure that it’s okay (the Helms / Chilton’s / Haynes manuals tell you how to check it).

Next, check to see that your throttle plate is closed all the way. Take your intake off at the TB and check to see that nothing is blocking the plate. If nothing is in the way and it isn’t closed all the way, loosen your throttle cable. Check to see if the nuts holding the TB and the IM on are tight, this was the source of my idle problem. If they are loose, tighten them. After that, check the idle screw. It’s on the top of the TB right next to the red vacuum line in the first picture. It’s a flat-tip screw and most TB’s have it epoxied over. If your screw is not epoxied over try adjusting it. Some air bubbles may throw the FITV off and keep the valve open, so bleed your coolant by draining small amounts and pouring more in

Take the 3 10mm bolts out of the FITV (you don’t have to take off the coolant lines). Then take off the two 8mm bolts from the plate on the back of the FITV. Once the plate is off you will see a white plastic thing, screw that all the way in. This causes a lot of people’s hunting idle problems (it’s a source of a vacuum leak). Put the FITV back on and start the car up. If it still idles badly continue onto the next step.

Here is a write-up on the FITV. Clean the IACV screen(s). See Oz’s write up on G2IC. Make sure your car is completely warmed up. With it running, take the intake off the TB. There are 2 holes right in front of the throttle plate; these are the holes that feed the IACV (top hole) and the FITV (bottom hole). With your finger, cover up the bottom hole (there should not be any suction if your car is at operating temperature). If the idle goes down, the FITV is to blame; either get a new one or take it apart and screw the valve completely closed (I have only read of people doing this, so I don’t know exactly how). Also, you will have to keep the engine speed up yourself when the car is cold.

Next cover both holes up with your fingers. The car should sputter and die (or almost die). If it does then the source of your faulty idle is the IACV. Replace it. If you want you can test the IACV. Shut the car off and put Positive battery voltage to the black/yellow terminal (on the valve) and momentarily touch ground to the blue/yellow side. When doing this the valve should click, if it doesn’t, replace it. If when covering both holes the car still has a high idle, you have a vacuum leak somewhere. Again check the IM and TB nuts. You can spray carburetor ******* around those areas and if any gets sucked in (the engine will rev) you have found your leak. Another source of vacuum leaks are where the FITV and IACV connect to the IM. Either replace the gaskets or use silicone gasket sealant. If nothing has worked you should test your TPS. Probe the middle wire on the TPS plug (with the key on but not running, and the plug still connected to the sensor) with the positive probe on the voltmeter, and the negative probe to ground. You should have .5v with a fully closed throttle plate and 4.8v with it wide open. If the TPS is off, replace it. If, still, nothing has worked you might want to try a new ECU. This also is very unlikely, but worth a try. So now, if it still idles badly, go through the steps again.

It is very unlikely that you will end up needing to do all of these steps, you will usually have your problem fixed within the first few steps, but these are all of the possible causes to your problem. Remember, if you have problems with all of these abbreviations then search online, the best place to look is www.honda-tech.com, I’ve found most of the abbreviations in Helms and Chilton manuals before, so you can look there also.