Ash983

I have 2001 EX Civic Vtec. I'm having idle problems for few months now and it has gotten worse. Here is a quick background of the issue:

1. The RPM used to fluctuate between 400 - 800 after the engine warms up and driving for a while, it goes up and down a few times then it stops at around 650, I think. Sometimes it does not do that at all and the idle stops at 750 without fluctuating.

I took the ICAV out, cleaned it and put it back in. The problem remained the same. So, I bought a new Denso ICAV to replace it and the idle got worse! The car now idles at cold start and the RPM goes between 2000 - 2500. Once the car warms up, the car idles at high RPM at 1500. If I turn the car off after it warms up and turn back on, it idles fine and the RPM stays at around 750. As soon as I push and release the gas pedal, the idle goes up and down then holds at 1500. Even the slightest pressure on the engine like turning the steering wheel all the way, it causes the idle to go up and down.

I put the old ICAV back on and it was exactly the same new issue! I cleaned the throttle body and it is still no improvement. I tried the relearn idle thing this morning by starting the car on cold and keep it at 3000 RPM until the fan engages then stop and let the engine idle for 5 min. No changes still!

Any suggestions of what to do next? Does my car have a cold idle control that is different than the ICAV?

Thank you

NDNV

Do you still have the Bosch O2 sensors on the car?
Did you end up swapping the gauge cluster?
Do you have any DTCs and a CEL on?

1. Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.
2. Check the engine speed at idle with no-load conditions: headlights, blower fan, rear window defogger, radiator fan, and air conditioner are not operating.
Is the engine running at 730 50 rpm?
YES - Intermittent failure, system is OK at this time.
NO - If the idle speed is less than 680 rpm, go to step 3; if it’s 780 rpm or higher, go to step 4.
3. Disconnect the IAC valve 3P connector.
Does the engine speed increase or fluctuate?
YES - Adjust the idle speed. If the idle speed will not adjust properly, clean the
passage in the throttle body, and then adjust it again.
NO - Replace the IAC valve.
4. Turn the ignition switch OFF.
5. Remove the intake air duct from the throttle body.
6. Start the engine, and let it idle.
7. Put your fingers on the lower port in the throttle body.
Does the engine speed drop?
YES - Check the idle speed. If it’s out of specification, replace the IAC valve.
NO - Check for vacuum leaks with the throttle valve completely closed, and repair as needed.

Ash983

To answer your questions: I know that the lower stream sensor is NGK but I don't remember if I replaced the Bosch upper stream sensor with NGK too! I will double check that later today. I did not replace the gauge cluster and I have a CEL code for IACV. I think the code was P0505.

If the upper O2 sensor is a Bosch brand, do you think that might be the issue? I will follow your steps to further narrow down the problem and I will post when I find out. Thank you so much again for your recommendations.

NDNV

If the code is indeed P0505 then the troubleshooting for that code is what I posted in post #2.

If you have the other IAC valve code at the same time (P1519), then there is other circuits, grounds, connections, loose terminals and open in the wire areas to look at.

I think I would always use Denso O2 sensors in this vehicle to avoid problems. Bosch brand has been known to cause issues and since the O2 sensors feed info to the PCM for air/fuel ratio, this Bosch sensor may be the culprit. Can you swap this one with a Denso to see if it makes a difference?

"The HO2S detects the oxygen content in the exhaust gas
and sends voltage signals to the PCM. Based on these
signals, the PCM controls the air fuel ratio. When the
oxygen content is high (that is, when the ratio is leaner
than the stoichiometric ratio), the voltage signal is lower.
When the oxygen content is low (that is, when the ratio is
richer than the stoichiometric ratio), the voltage signal is
higher."

Zedt3

Check your PCV Valve. A bad one can cause this issue as well.

Ohmega

iTrader: (1)

The fluctuation is a symptom, not the problem. The reason it is fluctuating is because if the engine is idling too high, the ECU cuts the injector PW.

Common cause for high idle is vacuum leak. Check all vacuum hoses and all along the intake tract for vacuum leaks.

Also, if you'd like to learn more about how the ECU "thinks" when it comes to idling, check out my thread -> https://honda-tech.com/honda-civic-d...-read-3263995/

Ash983

So after driving for 5 hours, I scanned the car and only one code shows up P0505. I removed the air intake duct and started the car. The idle was high and going up and down between 2000- 2800 (the outdoor temp is 21 F today and I started the car from cold). There is only one port by the throttle butterfly and when I covered it with my figures, the idle stabilized right away at around 1100. Moved my fingers away and the idle started going up and down at the original high RPM. I did this a few times and the idle was stable once without blocking the port. I give the engine a little gas and released to let it idle, it went back to the same crazy idling.

Does that confirm that the IAC valve is the problem? I just replaced this valve with a Denso brand and before I decide to return it, I'm wondering if there might something else that may be causing this idle symptom.

I didn't check the O2 sensor yet. We are expecting nice weather this weekend and will check that when I'm not slipping on ice.

Ash983

Great read by the way. Thank you so much for sharing it.

Ohmega

iTrader: (1)

1100 is still high for idle. Depending on where you live your idle should be anywhere from 650 to 850 with no load ( no headlights, a/c, climate control etc.)

I'd try adjusting your base idle, since it is free and will give you more clues as to what the problem is. I don't have a link for the procedure, but it should be pretty easy to find. Try this search- "2001 civic ex base idle adjustment" or something along those lines. The procedure is basically the same as other years and models, but I don't want to give you the wrong information.

Ash983

I will warm up the car first and check the idle. The car sat overnight in a snowy weather before I started the engine. It used always idle around 1100 as far as remember and slowly goes down as the engine warms up. Thanks for recommendation.

Ash983

So, I replaced the IAC valve with a brand new one and the idle did not change. I checked for vacuum leak using throttle cleaner and did not notice any change in the RPM. My last option is checking the PCV valve unless if someone has other suggestions to what else might be causing the RPM to go up and down. Thank you for your advise.

Ohmega

iTrader: (1)

Ash983

So, an update on this idle issue. I have changed the PCV valve and tried on two different new IAC valves and still the exact issue. The first new IAC valve did not fix the issue and I thought it was defective, so I got a new replacement.

I checked for leaks again and I found none. I was so convinced the whole time that it was the IAC valve after I checked for leaks and replaced the PCV. So I decided to make a short video of the idle issue that I'm facing here. https://www.youtube.com/watch?v=OZgV...ature=youtu.be

I reset the ECU and tried idle relearn a few times, but still no luck so far! Any more suggestions to go from here? TPS maybe? I'm thinking to replace the whole throttle body. Is that a good idea? I should mention that a while ago, I cleaned the EGR valve and not sure if it may have a connection to the idle issue!

Thanks again.

roguetwo

complete newb here but I had a loping idle on a 93 civic ex years ago. I tried everything and was creeping forums like you wouldn't believe. Finally I found a thread about the throttle body. They said take it off and inside there is a white, half dollar sized plastic screw/plug that gets loose. Tighten it back in and problem solved.

I don't know how much change there is in the model years or if you have already tried this and I have no idea what any of the valves you are talking about are, but the above procedure fixed my issue.

after googling parts it must not have been in the throttle body. I remember having to take off the air intake and then the throttle body to get to whatever contained that screw.

Ash983

Thanks for your suggestion. I think you are talking about the cold air valve with the wax adjustable screw in the middle. I don't have his valve in the car model I own. This idle issue is driving me crazy since I can't point to the exact cause yet. I will keep digging for more suggestions and hopefully I will find a solution to share here.

Thanks again anyways.

Rick hybrid

I cleaned the EGR valve and not sure if it may have a connection to the idle issue!


how many miles on the engine?
did you use a new gasket when you put the egr back on?
buy a can of carb cleaner spray and spray it thru the throttle body.
check and replace the rubber hoses, sounds like you have a vacuum leak

Ash983

Hi Rick. I've over 149K on the engine. When I cleaned the EGR valve, I did not replace the gasket, I don't remember seeing one to be honest. I used carb cleaner and whipped the EGR well then put it back on.

I will for sure take the EGR off again and look for the gasket. I'm guessing there is one on this thing!

Thanks for your suggestion.

NDNV

"If your Accord or Civic has a P0505 code, there are three likely causes:
1.The IACV-AAC valve harness is open and allowing moisture inside
2.The IACV has a poor electrical connection, or
3.The idle air control valve itself is faulty

Other Honda models that can sometimes have this issue include the Odyssey minivan and the Honda Pilot, both of which have technical service bulletins (TBBs) listed for them that any repair shop can access for more details.

For the driver, a P0505 code will usually mean that the engine becomes hard to start, runs roughly, or idles erratically. The engine may also shut off (choke out or stall) at stop lights after being driven to temperature (e.g. only after the vehicle has "warmed up").

The IACV controls the engine's idle speed at a specific level. When the engine is cold, the car will idle at a higher speed so that the engine can warm up as quickly as possible. This way, emissions control systems can reach optimum operating temperatures as fast as possible. The IACV manipulates the idle speed by controlling the amount of auxiliary air that enters the engine from the bypass passage...more air means faster idle.

If the IACV isn't working correctly, the engine can be starved of oxygen...this causes the symptoms (rough idle, stalling, etc.) described above. Often times a short-circuit is the cause of an IACV problem, so it's a good idea to check the wiring harness first when diagnosing the problem.

Occasionally, the valve itself may be blocked or stuck and require replacement. Whatever the issue, a simple diagnostic of the wiring harness and circuit is usually all that's required to locate the problem.

Author Jason Lancaster is the editor of AccurateAutoAdvice.com as well as a blogger for HondaPartsOnline.net. When Jason isn't writing about idle air control valves (or some other automotive topic), he's watching NBA hoops or spending time with his family."

Also this thread: Idle Surge Solved!! Everyone Please Read! - Honda Civic Forum

Ash983

Thank you for great write and sharing an interesting read about this issue. I was checking for vacuum leaks again today using carb cleaner and my the engine almost died when I sprayed at the bottom of the EGR! It took one spray to cause that to happen and I am wondering if that is normal or not. Could this be the reason why I'm having the idle to go up and down? I have only code p0505 and no EGR faulty codes!

NDNV

Sounds like you might have found the vacuum leak at the EGR valve. I've read that a bad EGR valve can act like as a vacuum leak. Odd you do not have an EGR code though.

Ash983

Changed the EGR gasket the other night and problem solved! No erratic RPMs at idling anymore and so far no ECU codes!

Thank you everyone for all of your feedback.

NDNV

That's great! Thanks for posting the solution.

agb22

May I ask why swapping the gauge cluster matters? I've been having the same Idle issue and I did change the bulbs behind the gauges before the problem started. Thank you for your help!

NDNV

The replacement of the gauge cluster bulbs would have no effect on solving an erratic idle.
I asked if the cluster was swapped from reading his history of posts to get an idea of what was performed already.
What are your symptoms, any codes with a CEL, what have you done so far? Lots of good ideas in this thread for solving an erratic idle.

agb22

I own a 1999 Honda Civic EX. D16Y8 Engine. The engine light has been going on and off with the same code for the Idle Air Control. The car had high idle when I started it up. The Idle would also go between 1500 to 1700 rpm while Idling. Then the car started dropping rpm while driving. For example, driving ~35mph @ 3000 rpm, the rpm drops down to 1500, back up to 2500, down to 1500, back to normal driving. It happens after the engine is sufficiently warmed up and I am basically coasting at one speed. The car feels as if it is about to stall out then comes back to life. I suppose it might not be exactly an idle issue because its happening under load. Engine light code is P0505: Idle air control system. This is what has been done so far:

- Checked made sure there is no air in the cooling system
- Smoke tested the engine, no vacuum leaks.
- Cleaned and checked throttle body
- Replaced gaskets on IACV and TB
- Replaced IACV
- Voltage tested all the sensors, all good.
- Checked PCV valve, working properly and cleaned.
- Timing Belts and Water Pump working properly
- Tried Resetting base idle, didn't help
- No problems with fuel lines

Probably going to buy a used ECM and install that because that is what multiple mechanic friends of mine have recommended. If that doesn't help, which i'm hoping it does, where should I go next? Clean the EGR?

Thanks for your help!