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1992, Honda Civic VX 5spd M/T
So, I’ve had idle issues before now on this car already. However, today the drive was strange. During the first part of the day, a few trips(mostly 8-10 miles or so), the RPMs in gear at typical speeds were reading about 400-500 too low for what I’ve ever experienced with this car.
It runs fine, has stalled once on a hard stop, but otherwise okay. I just did a top off of coolant, bled the system recently of air at the same time.
For example, 4th gear usually at 40 MPH is around 1400-1500 RPMs or so. Today it was struggle to be at 1000. I’m thinking ICM(Igniter) could be showing signs of going? Also, during this symptom when depressing the clutch pedal the RPMs want to stall between shifts and at idle the tachometer for the RPMs doesn’t seem to move at the lowest idle point and almost seems to be getting an inaccurate signal at these low points because I hear the engine change in speed but don’t get movement on the tachometer.
If I’m not mistaken, it gets the signal from the ICM on my vehicle.
But get this, later on today, suddenly the RPMs are normal again. 50 MPH in 5th gear is closer to 1500 RPMs instead of a 300-400 rpm fall off earlier in the game. It seems to fluctuate a tiny bit. I’ve noticed a random ‘tick’ in the RPM needle before and it has done strange before coming to a stop at idle/going to neutral before putting in gear again and then it would do fine. Might be related to cold-start or something, closed vs open loop? The idle RPMs were fine again, reading above the stall mark finally!
Any tips, things to diagnose?
Thank you.
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Sounds like it could possibly be the idle air control valve or possibly throttle position sensor as well. Are there any check engine lights on? What is the make, model and year? How many miles on the vehicle and how long since the last tune up?
Ok, so I edited the first post to include vehicle information.
268k miles, last ‘tune-up’ was the distributor cap/rotor with new OE plugs/wires back in 2010. I have since replaced the plugs again last summer. Replaced fuel filter a year ago. Air filter is fine. I notice some black oil-like substance around the TB/main air intake pipe that joins it when I remove to clean the throttle body at times.
Idle air control valve was suspected before, I got a brand new Denso OE part installed earlier this summer.
Lastly, I’ve adjusted the idle screw since it was tampered with before in an attempt to adjust the low idle RPM. However, the tach has only recently started ready strangely. I didn’t truly confirm anything like this until yesterday.
So, maybe I unscrewed the base idle screw too much and the IACV is trying to choke the engine too much or I have a vacuum leak somewhere? I’ve tried the method of spraying all around the intake for leaks. Nothing.
This is the only Civic prior to 1996 to utilize an EGR system and it is the only one to have a Constant Vacuum Control assembly, also does not have a FITV.
EDIT: There is no CEL. I replaced the 02 sensor, a 5-wire wide-band, about 2 years ago now however. It had a CEL at the time for it. No codes since then.
Do NOT mess with the TPS they hardly ever go bad so put that on the bottom of the list. The first thing that came to my mind was the IAC but if it’s new perhaps that’s a dead end as well.
Idle issues are mixture issues so if you have an idle problem it’s usually too much air or not enough fuel. Since Honda’s rarely have problems with fuel delivery I would say start by checking for vacuum leaks. It’s also VERY important that there isn’t any air in the cooling system, if there is then it can upset the idle.
Here is my ‘idle speech’ that covers a lot of the issues and also has some videos that might help.
As an aside older Hondas did have an EGR, they used them on the automatics but not on the manual transmission cars.
By suggestion I’m going to post my idle speech along with a couple of video links that I hope will help if your having problems with your Honda’s idle. First I’ll give you the link to the Solving Honda Idle Problems video, please remember that adjusting the FITV is the LAST step in the process and you need to back it off at least 1/2 turn after it bottoms out or it will not start properly when cold.
The Bleeding a Cooling System Video
The video response to the Honda Idle video
http://www.youtube.com/watch?v=AMjQry8mz-E&feature=watch_response
Lastly here is the “Idle Speech”
There are a lot of things that can contribute to an idle issue, in fact in the end it may still be there to some degree because of the nature of a 4 cylinder engine however here are some things to start with.
First start with a good tune up, use NGK or Nippon Denso plugs, don’t change the wires if they are OE, if they aren’t OE you might consider NGK wires as they are very good and less expensive then OE. A quality cap and rotor should be good. A new air filter also helps.
Don’t change the PCV valve, if you see an aftermarket PCV valve in there put a Honda in, believe it or not I’ve seen idle issues caused by aftermarket PCV valves, the OE’s last just about forever so you can easily justify the expense.
Next a good valve adjustment, this goes a long way to smooth out the idle if done correctly, mess it up and things can get a lot worse though.
While you have the valve cover off check the timing belt tension, if you feel a lot of slack this can cause the cam to ‘chunk’ as it spins causing a rough idle. If you think the belt has been on there for some time then you might consider changing it and resetting the tension properly, if it’s not ready for replacement you can reset the tension to take up the slack.
DO NOT adjust the idle screw under any circumstances, it is set at the factory and that is the reason it was sealed in the first place. If you find that the seal has been broken and you have a low idle and you have done all of the above then you might turn the screw out a little to see if that helps the idle but only enough to try and bring it back to where it was before it was adjusted in the first place.
Last clean the screen in the Idle Air Control valve, this can get clogged up with carbon over time and cause the flow through it to be restricted which can cause idle issues.
If you still have a ‘rough’ idle after all of this THEN look to the engine mounts as you want to be sure the engine is running correctly before you go for those as the one in the back is a real pain to replace.
I hope this info is helpful as I get a TON of questions about Honda idle problems, thanks for reading.
Hi, Eric. I’ve posted issues on my vehicle before on the old forum. It was the same suspected IACV issue, I tried to do the method of finding vacuum leaks but so far no success. Could my tachometer for the RPMs be flaky, though?
I was curious as to why the RPMs would read low when in gear during warmup and then higher later? This was soon after I recently topped off and bled the cooling system. This is about my D15Z1 that has the suspected headgasket leak which I then showed pics of the valvetrain and reported back as having good compression and data suggesting it’s at least not into the combustion chamber.
I’ve since suspected it’s possibly at an oil drain back between the head gasket and the block, instead of coolant into the combustion chamber.
However, I’ve since added a UV dye to my coolant this last time I topped it off. It’s losing about 1 quart every 1,000 miles; when before it wasn’t losing any.
You may recall the RTV sealant the PO used when replacing the thermostat before? I have a new OE stat I may just install to get rid of the sealant since it may be affecting the cooling system’s ability to get all air out if the small hole is plugged in the housing by RTV.
I haven’t had this low RPM reading since this posting and since it went back to normal RPM range during operation the other day.
It’s really strange. Usual RPMs are about 40 MPH, 1,500 RPMs in 4th gear. It was down to near 1,000 that morning. Power was zapped. Then later on, the trip home from the morning drive, it’s all good.
PS: This car doesn’t have the fast idle valve. Only the IACV, the new one looks like a legit OE Denso. Slightly different but same p/n as the older one I removed from the car. No CELs. Also, after removing the patch job someone did on the idle screw(the factory set one), I had backed it out about 3/4ths of a turn in an attempt to get the tach to read higher while setting the base idle. Would this cause the IACV to choke the engine if it was backed out too far to simulate a vacuum leak? Where else besides hoses and gaskets along the Intake Manifold could I do the spray and listen for engine change in detecting a vacuum leak? Is it worth pulling the cover to the Constant Vacuum Control box off and spraying around that old plastic solenoid(the one different than the EGR)?
Lastly, would a sticky EGR cause idle issues or hesitation to the point of lower RPMs ‘in gear’ like I experienced?
I did the bleed before this occurrence exactly as outlined in the video. I’m stumped man. This is why I want to learn how to gather more data to rule out other things. I guess engine RPM will do whatever it wants regardless of gear it’s in? It could be I didn’t bleed all of the air out, especially if the RTV in the housing for thermostat is causing problems. I have a new one and may just replace it during next oil change when I inspect with a black light for external UV dye leaks that I added to the cooling system.
Will report back on leak and if thermostat change/subsequent bleeding of air corrects the current symptoms.
Also, I have an aftermarket fuel filter and PCV valve in place. Thinking of going OE on both and removing that breather chamber, inspecting the PCV hoses to make sure there isn’t blockage.
Forget the EGR I don’t believe it has anything to do with your idle problem. As the “Idle Speech” states the idle screw should never be adjusted as it is set at the factory and if it’s adjusted the IAC may not be able to compensate for the changes to base idle. If the problem is intermittent I would suspect the IAC but as stated you might verify this by taping on the IAC as the problem occurs, if the idle changes when you do this then replace the IAC and recheck for the symptom. Follow the service procedure for your vehicle to reset base idle. Also NEVER use RTV on the thermostat gasket for the very reasons you mentioned. Most important is that you get all the air bled out of the cooling system, see the ‘Re How to Solve Honda Idle Problems’ video that I posted for you as to why. As for combustion leaks I don’t often find compression tests to be accurate in finding head gasket leaks, I prefer the method I show in this video.
Yeah, the Previous Owner left that stat that way. No idea how long. It could be causing some issues.
When checking for coolant leak, the pressurized cooling system(to like 17 pounds) didn’t lose any pressure and no leaks were found.
Also, I wish the Previous Owner/mechanic didn’t adjust the factory idle screw either. Can’t really help that now.
No you can’t help that now but it could contribute to the problem as well as RTV floating around in the cooling system possibly causing an issue somewhere. Idle issues are mixture issues so it’s either a problem with too much or too little air to the fuel that’s being added. That problem could be electronic due to false readings or issues with a bad actuator, it could also be in the case of an idle problem an issue with the coolant, air in the cooling system, or something that’s out of adjustment. Mostly what I find is poor quality parts or poor repair procedures that cause problems like that.
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