[aborremans]

Hi, I'm new to this form but so far everyone seems fairly knowledgeable. I currently am driving a 1989 Honda Civic LX 1.5 with M/T PGM-FI and 181,000 miles. Recently, when my car reaches it's normal running temperature, my car will began to idle erratically, almost like it is "hunting" for where to idle, usually between 1500 and 3000 RPM. I only have the problem after the car warms up to it's normal running temperature, not before. Most of the time the idle is consistently in flux, going up and down between 1500 and 3000. The idle also will at random stick and not idle down, but will only do this temporarily for about 30 seconds. Lastly, some times, when I shut off the car and get out I smell a little gas fumes from exhaust. I immediately changed O2 sensor and still have problem. So far I have:

1) Checked Throttle Cable, it's not sticking and working fine

2) Took the Idle Air Control Valve (IAC) off, it was quite dirty, I cleaned it out with throttle body cleaner. Problem remains the same, although idle does not seem to jump or fall as fast.

3) I recently re-soldered my main relay (fuel injection relay?) as I was having issues with it supplying power to ECU and fuel pump.

4) Attempted replacing ECU. No change in problem.

5) Found throttle cable over adjusted. Readjusted throttle and idle to where they should be, problem continues.

6) All the other "obvious stuff" such as air filter and fuel filter and O2 sensor checked.

7) Took my ICM to Autozone and had them test it... It's working just as good as the day it was put on the car

8) Replaced Coil as it went bad

9) No CEL coming on or codes flashing on ECU

So I guess my question is tri-fold. First, under any circumstances, could my main relay contribute to problem as it supplies power to fuel pump (i.e. when relay heats up it starts to send irregular voltage to fuel pump?) Second, Haynes repair manual states that leaking EGR valve lead to "erratic" idle, but says dealer must check it, is there any way I can test it without taking it in to a specialty shop? Third, is there a way I can test my IAC Valve to see if it is working like it should? I've officially checked everything I can think of and I am confused... Thanks =)

-Alex

[Duane in Japan]

You have not mentioned testing the Fast Idle Valve Solenoid, it looks like its mounted on the back of the intake manifold, drivers side, I am guessing that the top hose should not have vacuum when the car is warmed up, use a pair of pliers to squeeze this hose and see if the idle calms down. Let us know, I am also guessing if you unplug the connector, it may stop fluctuating also. Try both of these please and let us know.

[TxGreaseMonkey]

It's likely a vacuum-related problem. I'm sure you have checked hoses, EGR, et cetera for leaks. That pretty much leaves the IAC Valve and the Fast Idle Thermo Valve. My focus would be on the latter. When the engine is hot, check that the Fast Idle Thermo Valve is completely closed. If not, air suction can be felt at the lower port in the throttle body. If any suction is felt, the valve is leaking and needs replacing--it's not serviceable.

[Duane in Japan]

Txgreasemonkey, I guess I could have looked up the wrong year, is this like most FITV with the throttle body, I showed it as a solenoid on the other end of the intake. Hell I could have pushed 86, but I don't think so??

[TxGreaseMonkey]

I believe it is.

[aborremans]

Hey thanks for the quick response guys. I hope your having a good Thanksgiving! I don't mean to sound stupid, but I could not find my FITV, I looked and felt under and around my throttle body to no avail. I broke out a mirror to get a better look under my throttle body but did not see anything. I also attempted to trace coolant hoses hoping to find it but no luck. There are two coolant hoses that seem to go directly into my throttle body on it's underside. Is it possible that my model of car does not have a FITV? I tried searching for the part on Autozone and Advanced Auto Parts Website to see exactly what it looks like but they do not list it as a part for the car... Any idea's of what to do or where to look next?


-Alex

[Duane in Japan]

Use a hand pump vacuum pump from Sears, hook it up to the top of the EGR valve and vacuum the EGR diaphram, when it lifts the EGR valve, the engine should stall.

If your FITV is under the throttle body, remove the intake hose and you will see two holes just inside the throttle body, one near the top and one near the bottom, with the engine fully warmed up and the idle is hunting, put your finger over the bottom hole, if the idle settles then the FITV is leaking internally. If your FITV solenoid is at the other end of the intake, on the back side, then unplug it and see what happens then squeeze the rubber hose to see if the idle quits hunting. Let us know what style you have, I may have looked at the wrong car in the book, I was doing a hundred help requests.

[aborremans]

"I don't mean to sound stupid, but I could not find my FITV, I looked and felt under and around my throttle body to no avail. I broke out a mirror to get a better look under my throttle body but did not see anything. I also attempted to trace coolant hoses hoping to find it but no luck. There are two coolant hoses that seem to go directly into my throttle body on it's underside. Is it possible that my model of car does not have a FITV? I tried searching for the part on Autozone and Advanced Auto Parts Website to see exactly what it looks like but they do not list it as a part for the car.... Any idea's of what to do or where to look next?"


I'll check my EGR... thanks for the know how. Is their a way I can post pictures on here if I take pictures of my throttle body and intake manifold on here?

[Duane in Japan]

Look on the other end of the intake manifold, on the back side, towards the top, a solenoid with wires (connector) and a vacuum hose or two, if only one hose then the other vacuum port is its mount point to the intake manifold, probably just two wires also. Squeeze the vacuum hose with pliers and see if the idle settles down, then try another test of disconnecting the electrical connector and see if it calms down.

Do you have a pic website that holds your pics for you, just link to there.

Webshots - Free Online Photo Albums and Photo Sharing!
I upload mine here.

My Public Shoebox pictures from friends & fun photos on webshots
Put the pics in My Public Shoebox when loading from the site above in the first link, I had troubles navigating the site so I linked to the Shoebox directly so I could link my pic to the forums.

There are other well known pic holding sites, I just chose this one, click on your pic, copy the address bar address and paste it in your response if that is all you can do, takes some practice with these things sometimes.

[dscivic91]

Your idle problem is more than likely to be an air pocket so just bleed the air off and add water and should fix your problem and the no power problem is your main relay

Hi, I'm new to this form but so far everyone seems fairly knowledgeable. I currently am driving a 1989 Honda Civic LX 1.5 with M/T PGM-FI and 181,000 miles. Recently, when my car reaches it's normal running temperature, my car will began to idle erratically, almost like it is "hunting" for where to idle, usually between 1500 and 3000 RPM. I only have the problem after the car warms up to it's normal running temperature, not before. Most of the time the idle is consistently in flux, going up and down between 1500 and 3000. The idle also will at random stick and not idle down, but will only do this temporarily for about 30 seconds. Lastly, some times, when I shut off the car and get out I smell a little gas fumes from exhaust. I immediately changed O2 sensor and still have problem. So far I have:

1) Checked Throttle Cable, it's not sticking and working fine

2) Took the Idle Air Control Valve (IAC) off, it was quite dirty, I cleaned it out with throttle body cleaner. Problem remains the same, although idle does not seem to jump or fall as fast.

3) I recently re-soldered my main relay (fuel injection relay?) as I was having issues with it supplying power to ECU and fuel pump.

4) Attempted replacing ECU. No change in problem.

5) Found throttle cable over adjusted. Readjusted throttle and idle to where they should be, problem continues.

6) All the other "obvious stuff" such as air filter and fuel filter and O2 sensor checked.

7) Took my ICM to Autozone and had them test it.... It's working just as good as the day it was put on the car

8) Replaced Coil as it went bad

9) No CEL coming on or codes flashing on ECU

So I guess my question is tri-fold. First, under any circumstances, could my main relay contribute to problem as it supplies power to fuel pump (i.e. when relay heats up it starts to send irregular voltage to fuel pump?) Second, Haynes repair manual states that leaking EGR valve lead to "erratic" idle, but says dealer must check it, is there any way I can test it without taking it in to a specialty shop? Third, is there a way I can test my IAC Valve to see if it is working like it should? I've officially checked everything I can think of and I am confused.... Thanks =)

-Alex

[aborremans]

Okay... A long overdue update. I figured out what the problem was with my erratic and annoying idle. After eliminating every possible mechanical issue which might affect the idle I was forced to conclude that it was an electrical problem of some sort. After swapping ECU's and many a fustrating afternoons with my trusty multimeter I shifted focus out of desperation to the FR signal of my alternator. The signal was fine. I was stumped.

One day, as I was listening to Car Talk and they mentioned that the Coolant Temperature Sensor (TW) (also known as an ECT) can affect high and surging idle. I was curious, what about a simple sensor that monitors the temperature of my coolant could cause a surging idle? I thought it was just there to let me know if my car is overheating. As it turns out, it matters a lot.

After a little research, it seems your ECU puts a 5v load on the TW sensor, the sensor resists the amount of voltage that passes through as the engine as it warms up. The ECU in turn reads the variance of voltage and responds by adjusting the pulse width of the injectors to run a rich mixture when the engine is cold, and lean when the engine is at its peak operating temperature.

Sure enough, I checked my sensor and I was getting vary erratic readings when the sensor was warm. I also was not getting any CEL codes telling me that the sensor was failing or bad, and I tried two different ECU's when diagnosing the problem! So after a $26 Autozone part, my car idles smoother than ever, and I imagine I'll be getting better gas mileage as well.

I haven't seen anyone yet post this as a possible problem for idle issues in Honda cars on this forum. Hope this helps some other frustrated DIY guys at home... thanks again for your help everyone!

-Alex

[TxGreaseMonkey]

Thanks for the update. That's good information to know, since so many people have had problems with erratic idle on this site.

[graywhale]

I had the same behaviour on my 1989 Honda Accord LXi - rev up and down when warm. Very annoying. But the fix was easy:

What you most likely have is a dirty IACV a.k.a. Idle Air Control
Valve that causes this. The sensors there can get dirty sending erratic signals. So I cleaned it without even uninstalling the thing, just loosening the two bolts and using a straw from the spray cleaner to get inside and in between the crack to clean the sensors and viola, the engine runs like new.

Just be prepared for the rubber gasket to fall out. You'll have to fish it out and place it back as best you can before tightening the two bolts again.

Here's more on this issue:
How To: Clean Your IACV - Team Integra

[Duane in Japan]

I have been away from my computer for several months while moving two times and 11 grand later, I am finally back in my own computer with my own database. The TW sensor is one of the first things checked along with the actual coolant level and be sure there is no air pocket in any of the idle control devices, sorry I couldn't give this info before.


High Idle speed and Fluctuation troubleshooting

Leaking EACV- Disconnect EACV connector. Idle speed should decrease. With the connector disconnected block the hole in the intake port or pinch the hose from the air cleaner to the EACV. If the idle speed decreases the valve is leaking. This condition will not set a code. The ECM can only detect an open or short circuit. It also may clog it’s screen if it has one.

Leaking IAC- (Idle air control valve) Disconnect IAC connector. Idle speed should decrease. With the connector disconnected, block the hole or pinch the hose to the IAC valve. If the idle speed decreases the valve is leaking. May not set a code and may not be a codeable circuit on all models.

TW or ECT sensor- (engine coolant temperature sensor) voltage should be about 3.0 volts @ 60 deg F and between .55 & .7 volts @ normal operating temp. If the voltage is above .8 volts at normal operating temp, will cause rich mixture and high idle speed. May not set a code because it is not far enough out of its operating parameters. **Also this sensor will not read temperature correctly if coolant is low. (beware)

Vacuum leaks- a loose vacuum hose or leaking intake manifold gasket can cause high idle speed and/or fluctuation. Also check for bad PCV valve.

Fast Idle Valve- (if equipped) a fast idle valve that is sticking can cause high idle speed and fluctuation. Check it by removing the steel cap on the top and putting your finger over the hole in the middle of the seat under the cap or block the port just inside of the throttle body opening, when the Idle is fluctuating or staying high. When the engine is warm this valve should be closed. You can tighten the seat but it will also change the idle speed warm up values (closing).

Throttle valve- throttle position sensor voltage should be .5 volts with the throttle closed. Make sure the throttle valve is fully closed and voltage is within spec.

ECU-If all else is good, if you reset the ECU and the problem goes away temporarily, the ECU may be defective.

Verify that the cooling system is full of coolant and
there is no air in it.

Remove the air boot from the throttle body and cover the
throttle body with something that will stop the airflow
(your hand, tape) with the engine running. With the
throttle body covered and no air going into the engine, the
engine should stall. If the engine does not stall, look for
a vacuum leak. With the engine running and the coolant
temperature above 90 degrees F, verify that there is no
vacuum on the lower port in the throttle body. If it does
not lose vacuum, look for a faulty fast idle valve on the
bottom of the throttle body, as long as the coolant hose is
good and hot.

Verify that the base idle screw was not turned way out on
the top of the throttle body. If it was, set the base idle
and see if the problem still occurs.

The upper port in front of the throttle plates feeds the
Idle Air Control (IAC) valve and the base idle screw. If
the IAC is unplugged and the base idle screw is turned all
the way in and there is still airflow through the upper
port, check for a stuck open IAC valve.

[sjsperry]

$26. That's all it was for me. Thanks to your post and Duane in Japan's testing procedure, I only spent a couple hours today getting it all right. Awesome work sisters.

Okay... A long overdue update. I figured out what the problem was with my erratic and annoying idle. After eliminating every possible mechanical issue which might affect the idle I was forced to conclude that it was an electrical problem of some sort. After swapping ECU's and many a fustrating afternoons with my trusty multimeter I shifted focus out of desperation to the FR signal of my alternator. The signal was fine. I was stumped.

One day, as I was listening to Car Talk and they mentioned that the Coolant Temperature Sensor (TW) (also known as an ECT) can affect high and surging idle. I was curious, what about a simple sensor that monitors the temperature of my coolant could cause a surging idle? I thought it was just there to let me know if my car is overheating. As it turns out, it matters a lot.

After a little research, it seems your ECU puts a 5v load on the TW sensor, the sensor resists the amount of voltage that passes through as the engine as it warms up. The ECU in turn reads the variance of voltage and responds by adjusting the pulse width of the injectors to run a rich mixture when the engine is cold, and lean when the engine is at its peak operating temperature.

Sure enough, I checked my sensor and I was getting vary erratic readings when the sensor was warm. I also was not getting any CEL codes telling me that the sensor was failing or bad, and I tried two different ECU's when diagnosing the problem! So after a $26 Autozone part, my car idles smoother than ever, and I imagine I'll be getting better gas mileage as well.

I haven't seen anyone yet post this as a possible problem for idle issues in Honda cars on this forum. Hope this helps some other frustrated DIY guys at home... thanks again for your help everyone!

-Alex

[Gapeach10]

Your problem seems to be the TCU (transmission control unit). It is usually located in the floor board of the passenger side.

[HondaFreak101]

Had the same problem with my prelude but when I changed my pcv valve it was sweet after that.