Hi,

This is a very tricky problem to diagnose and I have ran out of ideas.

I just bought a 2001 Honda Civic EX 1.7L VTEC with 163,000km (private sale) and have tried several things to fix this problem and ran out of ideas. I would really appreciate some help! I've read several forums about this and can't find any that cover this specific problem.

!! Please help !!


Low Idle - Before Timing Belt
1. For about a minute or two after turning the car on, it would idle nicely at around 1,000 RPM.
2. A couple minutes after driving it, it would idle extremely low, and if I came to a stop light, it would stall.
3. After 5 more minutes of driving, it would warm up enough that it would NOT stall, but it would idle very low, between 500 and 700rpm.

No check engine light and it was like this for about 2 weeks.

Had Timing Belt Done
I took it in to get the timing belt done and asked if they could have a quick peek at the idle issue.

Fluctuating / Irratic / Seeking idle
When I picked the car up, I drove away from the shop and the idle was doing very strange things. It would fluctuate up and down by about 500-700 RPM depending on how warm the car was. (Example: Cool - between 1500-2200 up and down cycle would take 2 seconds - and when warm, usually from 1000 to 1500 RPM with the same slow cycle. It would seem as if someone was pressing the gas, letting the RPM's get up, and then letting go of the gas, then repeating continuously.

I immediately took it back and the mechanic said that he thought it was acting a bit weird, but to try drive it around for a couple days to let the computer re-learn. He said the only thing they did was reset the ECU.

The check engine light came on within a couple hours of driving. I called the mechanic again and he said to bring it back in. He had another look and hooked it up to the computer and got the P0505 (Idle Control System) OBDII code. He said that it was most likely the idle control motor. The part was $600-$700 from the shop so he suggested trying to find a cheaper or used one somewhere.


I found one at a junkyard from a 2002 Honda Civic and replaced it myself. I reset the ECU to clear the engine code, and had the exact same problem with the used part. I found a new Idle control Motor from the USA for $197.29 and just put it in and have the exact same problem again. I thought this would have fixed it, and am very dissapointed that it did not.

Some of the Troubleshooting I've since done
Some interesting things I noticed.

*** When I start the car, before I touch the gas, it will idle around 1000 RPM for as long as I want. As soon as I touch the gas, the idle begins to seek or go up and down. It doesn't matter if the car is cold or hot.

*** If you let the car sit with the idle seeeking for a couple minutes, it seems to lock into a quick pulsating RPM range of about 1498-1502 RPM. You can barely see the needle moving, but can feel the engine pulsating. Pressing the accellorator will increase the RPM's, but the pulsating will continue - for example, pressing it a bit will bump it up to 1750-1754rpm.. Driveability at this point is very abrupt in the idle range. Accelerating from idle, or deccelarating to idle will cause the car to jerk almost violently.

*** If I turnt he car off at this point for a few seconds, and turn back on, it will idle normally at 1000rpm until you touch the gas, and then it will go back to the less annoying "Seeking" idle. It's very replicable. If i come to a stop light and don't press the gas every once in a while when the idle is seeking, the car will change personalities and go back into the pulsating mode.


*** I took the airbox off and looked at the throttle body adn cleaned the inside of the big port with carb cleaner on a blue shop rag but that didn't seem to help. I'm not sure if there is anything else in the throttle boty on this specific engine that would need cleaning - hoses etc??

but.....

I THINK MOST IMPORTANT CLUE...
when I plugged the hole in the inside of the throttle body that leads to the idle control motor, the car went back to a nice 1000rpm idle. If I engaged the throttle cable a bit, the idle would go back to seeking. I could replicate this indefinately. This is waht made me order the $200 part as I thought it was definately the idle control motor, since when I plugged it up, the car worked fine.


*** I also tried resetting the ECU, turning the car on with all electronics off, not touching the gas, and letting the car idle for 10 minutes to try teach it the idle. This did not help.

*** Put in new spark plugs (Bosch Platinum +4) and also some fuel injector cleaner and neither helped.

I have a OBDII code reader connected to my laptop, so I can get any type of information that you might find useful from the diagnostic software.


The P0505 and P0505* codes will come up after a few hours of driving with this issue. What other pieces of the puzzle can I look at? What else is part of the Idle Control System??


Could the timing belt be the issue? The car drives just like it did before the belt, except within the idle range.


Please let me know if there is anything else I can try or tell you that can help diagnose this.

I really appreciate any help with this as I don't want to keep taking it back to a shop.

Thanks


Jason

 

Make sure the radiator is completely full; air in cooling system will cause unsteady idle.

Take the idle air control valve off and clean it with carb / throttle body cleaner.

With the passage plugged, the idle should drop really low-- there may be an air leak.

If the car drives OK at speed, timing belt would be OK.

 

Thanks for the quick reply. It's good to know that the timing belt is fine if it runs fnie at speed.

Cooland: I actually did top up the coolant today before a 200km drive (it didn'tneed much) and no difference.

The idle air control valve is brand new (just put it in a few hours ago) so wouldn't need cleaning. This is the 3rd one (had original, junkyard, and new one).

Where would I look for an air leak? The airbox is secured and I tightened the clamp that connects to the throttle body.

 

Leaks would be into the intake manifold after the throttle body, such as vacuum hoses, throttle body to manifold gasket, and manifold to cylinder head gasket. Also that model may have a fast idle valve on the thermostat housing and those are very easy to break.

 

I don't think there is a fast idle valve. When doing a search on autopartsway.ca there are no results for a thermostat housing, and a google search said 1996 and newere don't have it...

You may be on to something with air in the coolant system becuase...

Some new issues that just happened.

I just drove back from my friend's house in -7 degree weather. The drive was about 13 minutes, and my car did not heat up at all inside and the engine temperature first got to normal operating temperature and stayed at that for about half the trip, and then almost reached "High" before I got home. The top radiator hose was quite warm - my hands were freezing so it was pleasant to hold on to, but not burning hot, and the bottom radiator hose was cold. There were a couiple more thinner hoses on the right side of the engine - one felt lukewarm, and the other cool.

Directly below there the top radiator hose comes out of the radiator and connects to something, there is an electrical connection that seems broken. There was coolant on this, and has been a coolant around this area since I bought the car, but very little. Could this be interfering with the thermostat operation?

With the weather getting colder recently, I have noticved that my heater has started to take longer and longer to warm up inside.

Do you think this is related at all to the idle issue? If not, I will start a new thread for this, but I'm no mechanic, so maybe these two things can be linked somehow...

Could an O2 sensor cause the fluctuating idle? My co-worker said he had that happen on his mitsubishi.

Thanks..

 

Thank for the respnoses so far.

Pleease disregard the last post. For some stupid reason, I thought filling up the reservoir with cooland was good enough, but I filled up the Rad and that part is working fine.

A couple people have mentioned vacuum leaks. I took the airbox off today and realized I have no clue what hoses to check for air leaks... How many hoses are there, and where are they?

While it was apart, I thought I'd check some of the sensors and when I disconnected one of them and turned the car on and to my amazement, the car SEEMED TO IDLE FINE, but would NOT REV HIGHER THAN 3500RPM.

I am not sure what the sensor is that I unplugged, but I got code:
P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage?

I am assuming this is the MAP sensor that I unplugged.

Any ideas why my car would idle fine when unplugging this? I also disconnected a hose that ran to the MAP before having the MAP disconnected, and tried running it with the hose disconnected, and plugged at either end and there was no difference, and I couldn't feel air coming out or being sucked into the hose, or where the hose connects...

Any clues or hints on how and where to check for vacum leaks, or do you think the sensor is bad and I need a new one of those?


I will post a picture of the sensor that I disconnected.

Thanks for helping!

 

To summarize....

1. Car idle fluctuates up and down by 500-700 RPM
2. Replaced Idle Control Motor with new. Still happens and I still get code P0505
3. When I turn on car, before pressing gas, car idles fine. Press gas once and car idle fluctuates.
4. If I plug the hole to the idle control motor with my fingers for 10-20 seconds, the car will idle properly again untill I press the gas.
5. Disconnecting the Mass Air Flow sensor lets the car idle fine!, but then it won't let me rev higher than 3500RPM. Check engine light P0108

I'm going to try clean the MAF with some MAF cleaner, but the screw is stripped and it's too dark to work on it. Hopefully I'm on the right track.

Any specifics about what vacuum hoses to check for leaks would be great. I don't know which ones are the vacuum hoses.

Thanks