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Thread: Throttle/idle Issues on 1987 Honda Accord LX

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    Throttle/idle Issues on 1987 Honda Accord LX

    Hello,

    I'm trying to correct some recently (last couple months) idling problems on my carbureted 87 honda. The car has 270k miles on it and I've had a lot of fun keeping it going/learning about automobiles with it. I've replaced the clutch, water pump, rebuilt the power windows and locks, replaced the fuel tank pump, installed new breaks/calipers, tie rods and CV joints and fixed some electrical issues all with the help of 3geez! Even with those successes I cannot adequately address my current issue. I will outline the symptoms below, describe what I've done so far and then make some guesses about what I should do next based upon everything I've read here in the threads: Idle Adjustment & Emissions Help, includes PCV and Black Box info, Vacuum Gauge Read, What Does It Mean? And Serious Problems, Loose booster Venturi/carb Icing/Throttle Stick/Dieseling and in my carefully examined repair manuals (Chilton 73-88 and 84-95 and Haynes 84-89).

    I would really appreciate advice and perspective. I am a student (biomedical) so I do not have infinite free time and would prefer to start diagnosing at the most likely places. Here are the symptoms as I know them:

    A) Engine idles lowest at 1100 rpms and often higher at 2500 rpms. When decelerating and coming to a stop the rpm will often increase further to 3000. The rpms do not increase unless the clutch is engaged. If the engine remains in gear the rpms behave normally as one would expect.
    B) The rpms do not decrease when the clutch is engaged while shifting gears or when the pressure is removed from the gas pedal.
    C) The engine will occasionally diesel upon shut down.
    D) Very occasionally (3 times total) the engine fails to idle. When the clutch is engaged and the car is decelerating the rpms will rapidly fall and the engine stalls. The engine will immediately restart as long as plenty of throttle is given. This symptom goes away with a few restarts and then the car idles around 1100 rmps.
    E) Occasional surge and galloping while accelerating in the first and second gears.

    Recap:
    High RPM that doesn't decrease with clutch engaged or gas pedal released.
    Surging/galloping during accelerating in first and second gears.
    Dieseling
    Stalling of engine during deceleration.

    My attempts to address issues:

    1) Replaced spark plugs, wires and air filter. Checked all coolant and oil levels.
    2) Adjusted the throttle cable. It is NOT to specifications: if the throttle cable is tightened to recommended deflection 3/16 to 3/8 of an inch the engine races at 5000 rpm. The throttle cable currently has ~2 inches of play in it (as I found it originally).
    3) Adjusted the idle speed adjustment/throttle stop screw. This had no discernible effect. Rotating it both clock and counterclockwise did not change the idle speed.

    My plans for correction:

    4) Check vacuum lines with a vacuum gauge checker. I have one ready to pick up from Harbor Freight. I will replace failed lines and solenoids. Any information as to what I should check first or what is the best reference material would be greatly appreciated.
    5) Check the throttle plates to see if they open and close w/out sticking (I need to figure out what/where these are).
    6) Remove the air filter, gold screen and look down the barrels (location unknown to me) and inspect to see if the secondary butterfly valve is open. Should this be done with the engine running and an assistant to run the throttle (I will be wearing safety glasses).
    7) Follow the test procedures in one of my manuals and conduct the tests for the choke opener and fast idle unloader.

    Should all these fail: purchase a weber carburetor (DGV 32/36), but the adapter plate, bolt it on and throw away "40 lbs" of emissions controls. Which I would be fine with as I am not concerned about emission controls (should I be? Car is and will remain registered in Alaska).

    Please let me know if I am barking up the wrong tree or making errors. Questions, comments and opinions appreciated.



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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    I'd start by finding out why the idle screw has no effect. If it's damaged, it can make things very interesting. Definitely check for vacuum leaks. For that, I would use a can of carb cleaner or suchlike instead of a vacuum gauge. Your throttle cable also sounds like it's having some issues (2" of slop?!).
    Dr_Snooz

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    How would I use carb cleaner to check for vacuum leaks?

    Would I spray it directly on the lines?

    Also I should have been more accurate about the idle adjustment. The idle screw can cause the engine to increase the idle but doesn't decrease below 1100 or 2500 rpm depending...

    I will be replacing the throttle cable with one from a pick and pull. Or a new one?
    Last edited by Deepdriller; 05-24-2014 at 06:40 PM.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Spray the cleaner anywhere there might be a leak. If the idle speed changes, then you know you have a leak. You'll be spraying around connections, gaskets and on any old, hard lines (which by now will be most of them).

    For the throttle cable, I'd say do a little more investigation to see why there is so much slop. It might just be a bent bracket, which is a free fix. If the cable doesn't slide freely through the housing, then it must be changed. I would buy new for myself, assuming you can find one that fits. Otherwise, get the best condition one you can find from the scrap yard. A universal fit cable would be my last choice. If you don't install them just right (which usually involves a lot of custom modification), they can kink and stick. Not good.
    Dr_Snooz

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    I used carb cleaner and sprayed all over the connections, gaskets and lines. The rpm were not effected by any spraying (unless it was directly into the carb causing the rpm to fall). I also replaced the throttle cable with a lower milage one (not as easy to do as the manuals described). While the cable was disconnected I tested the mechanisms and am confident that the throttle cable has nothing to do with the high rpm.

    I also checked the solenoids with a vacuum gauge. I checked the solenoids I could with it and they all held vacuum.

    I noticed the choke wasn't closing up. I think I read elsewhere that it should close up entirely. It doesn't. Here are some photos. Obviously you can smell a lot of unburnt gas in the exhaust.

    This is the carburetor right after the engine has been started with rpm 1900

    Attachment 6238

    After about 15 minutes of running, rpm at ~2500

    -running-~15-mins-rpm-2500-jpg

    After hour or so, the car heated up and with carb cleaner and all the other alterations rpm were at 3000.-rpm-@3000-after-being-hourish-jpg

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Your choke is not opening. It should be fully vertical after 15 minute warmup. Download the Honda Service manual available on this site. (Chilton's & Haynes are useless). For starts, just grab the choke opener puller and open the choke. Could be the vac leak is in the choke opener, causing the failure to open and high idle to hang.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Thank you for the information and advice. I have downloaded the Honda Service Manual and have begun to review the applicable sections. This manual is far superior to my books although they were good background information. Looks like I need to get a vacuum pump (I bought only a vacuum gauge).

    Does it matter what model car I have? Because I am not familiar with the manuals model abbreviations. How can I determine if my car is an A/T, KT, KP, KQ, KX, M/T or A20A2 model? I know it isn't the A16A1 because there is no choke cable.

    I have a 5 speed manual transmissions btw.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    It's clear from your pics that you have an automatic choke opener, so that is first suspect for the problem. You can cap off the 2 vac ports on the choke opener... and if the choke doesn't open, that is strong evidence that the opener diaphragm has a leak. ( you can also put your vac gauge on the port for 'cranking leak solenoid' while running and measure for vac here. Also, you can use the carb cleaner as Dr Snooz suggested, and spray just a tiny bit around the diaphragm where the puller arm enters the choke opener. This will feed right into the carb. Check a few of the other posts here about high idle problems,,, I have described my experience with troubleshooting many times here,.... But it sure sounds like you need a new choke opener. (that was my problem as well a few years ago)

    The other differences on the various models (at least with this vacuum circuit...) have to do with which thermovalve controls the secondary on fast idle unloader; Thermovalve A or B.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    I reviewed many of your's (and other's) previous posts on idling issues and based upon those readings I decided to check the fast idle unloader and the automatic choke via the manual's directions in sections 11-29 and 11-30 respectively. I used a vacuum gauge pump and checked the fast idle unloader (located towards the passenger compartment and non-driver side of the carburetor). The manual said to check the inner and outer fittings of the fast idle unloader for vacuum. No vacuum was found at either the inner or outer fitting. The manual also directed to apply vacuum to the inside fitting and see if the idle speed dropped. Vacuum on the inner fitting had no effect on the idle speed. I'm not sure what this means. Any idea?

    The manual said if no vacuum was observed on the inner fitting to check the automatic choke opener (located forward of the fast idle unloader). I plugged the inner fitting of the choke opener with my finger and applied vacuum to the outer fitting. This did not move the opener rod and had no effect on the movement of the choke valve.

    I think this means that, as you predicted, the diaphragm has failed and no longer holds a vacuum.So the choke is open all the time providing too much gas. I have examined the automatic choke opener and think I can remove and replace it. Seems to be held on only by three screws and the linkage. I saw you sourced yours from Majestic Honda. I looked for the part in their on-line catalog under accord - LX - KA5MT - but couldn't find anything. I can see the part in the carburetor section, but it doesn't have any number. Any suggestions?

    What do you think about replacing the automatic choke opener myself? Any tips/suggestions I should know? Should I check other things before I replace the part?

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    You may have trouble finding a new choke opener; looks like the part is discontinued. Maybe find new old stock (NOS).
    It is easy enough to replace once you find one.

    I would suggest one more test to be sure there are not other problems with high idle unloader or thermovalves.
    Get some bailing wire and carefully secure the choke valve wide open (vertical).
    Start and let the engine warm up completely.
    Unhook line #18 from the choke opener. ( it is the one on the small end of the choke opener, it is the one that does not go to the black box)
    Use the vac pump to pump line 18. It should pump down and hold vacuum, and it should drop the high idle unloader to normal idle. If it does not, there is another problem with thermovalve, high idle unloader, or a leak in this circuit.

    Don't drive the car unless the choke is fully opened(bailing wire or otherwise); running so rich will cause all kinds of other problems. Fouled Cat. carbon deposits everywhere, cylinder wash down, fuel dilution in the oil...

    Edit: Majestic Honda item 18 on the carb diagram is pointing to the choke opener. It's listed as 'diaphragm set', and discontinued.
    When I ordered I got the whole part. Maybe the leaking diaphragm can be replaced or repaired... It can be opened up.
    Last edited by g.frost; 06-18-2014 at 08:00 PM. Reason: add info

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    I found a choke opener from Auto Parts Warehouse. They didn't call it an Automatic Choke Opener. They called it a choke diaphragm. It is the same part though. -new-choke-opener-jpg

    I've used wire to secure the choke valve vertical. This does fix the idle issues and the engine idles nicely, but if the throttle is engaged the engine dies. Whenever the throttle is activated it causes the engine to quit. I can't figure out a way to have the choke wired open and be able to drive the car.

    I appreciate the advice about running the engine rich and have been driving as little as possible and never in traffic where the engine would have to idle at length. I intend to Seafoam the system after I resolve this idling issue too. Before I swap out the choke opener I will unhook line 18 from the choke opener and put vacuum to it to see if the idle drops. If it doesn't I guess that means checking the thermovalves A and B and maybe replacing the fast idle unloader?

    Here are some photos

    Vacuum tubes:
    -vacuum-tubes-jpg

    Me trying to get the rod to suck in via vacuum:
    -choke-open-check-jpg

    The position of the choke valve the car idles best:
    -good-idle-jpg
    Last edited by Deepdriller; 06-19-2014 at 08:03 AM. Reason: clarity

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Having the choke plate partially closed like the pic and it idles best usually means you're running a bit lean. Choke partially closing would bring the mixture back to what it supposed to normally when the choke is fully open. Are you 100% sure that there are no vacuum leaks somewhere? Have you checked the carb base and intake manifold to head? The intake gaskets are known to fail after 25 odd years.

    Do you still have high idle problem?

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Since you already have it, And with what you have do getting at the parts to test, ... I would go ahead and replace the choke opener and see how far that fix gets you. No idea about the stall just off idle, never had that problem, but you know about one vacuum leak; the choke opener diaphragm. Maybe, (if you are lucky) fixing that leak will also solve the stall problem.

    To clean up carbon & fuel deposits use a PEA detergent cleaner, full dose in the gas tank; Redline SI-1 or Techron.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    I pumped down line 18 and didn't see any drop in RPM. I decided to replace the automatic choke opener anyway and I while I was tinkering I noticed that line #4 had was torn. I replaced it along with a bunch of other lines. Probably about 4 feet of tubing all together combined with the lines I replaced earlier.

    It is a good thing, because as expected, the automatic choke opener diaphragm had failed:

    -hole-choke-opener-jpg

    Here is the opener broken down:

    -disassembled-choke-opener-jpg

    Here is a picture of the new choke opener installed and a bunch of the replaced tubes, some of the old tubes and the old gas pedal rubber cover that I replaced with a newer one from the pick and pull:

    -new-choke-opener-tubes-jpg

    -some-replaced-rubber-jpg

    Here is the new idle:

    -new-idle-jpg

    It is still a little high. I messed about with the idle adjust screw and could get the idle to increase readily, but when I tried to decrease it the engine wouldn't reliably stay running. I'm pretty happy with a 1100 RPM. I've seen other posts on the forum that mention 1000 RPM to be an excellent idle speed for this era of honda. It is certainly better than an idle of 3000 RPM. A lot less hard on my clutch.

    Thanks for all the help! Here's to the first 274450 miles. I hope to get it to 400,000 and beyond. If anyone has bright ideas on how to reliably further decrease the RPM I am all ears. Don't hesitate to comment/suggestions.
    Last edited by Deepdriller; 06-21-2014 at 10:31 PM.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Congrats on getting it fixed, and thanks for following up to let others know the solution.

    The 1100-1200rpm idle could be the second stage of the fast idle unloader hanging. 2 lines to the Fast Idle Unloader. 18 is the first stage that drops from 2000 to 1200rpm. Vac on Line 19 then drops from it from1200 to 800rpm. The 800 rpm is controlled by the idle screw in back of the carb. The Fast Idle is controlled by holding the throttle valve partly open; a cam on the fast idle unloader. (stop screw adjustable, I think....)

    Next time you are in there, see if you can tell if the fast idle unloader cam is letting the throttle valve completely close when warmed up.... Vac on 18 and 19 is controlled by thermovalve. 18 closes first letting the choke fully open (choke is 2 stage as well), then warmer still, 19 closes. You can put a vac gauge on 19, (where it connects to fast idle unloader, it should pull vac when warmed up. Now plug vac pump into port 19 of the unloader and see if it pumps down and holds vac.

    My thermovalve A is lazy sometimes in cold weather and will hang onto the 1200 rpm idle too long. Never an issue in summer though.

    When everything is right; spark, valve lash, (....and the carb is behaving), it purrs at 750-800rpm.

    (The 1100 rpm idle could be caused by another vac leak somewhere as well)
    Last edited by g.frost; 06-23-2014 at 04:28 PM. Reason: add info

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Mine would not go below 1500 RPMs and would be about 2200 on start, but after I did two Seafoam treatments it started to idle smoother and now it starts and stays at 750 - 800 on cold start. It sputters for a bit at the very start but gets very smooth after about 3-4 seconds. The seafoam also cleaned out the carb jets (I could see the crud lining them) as it wouldn't even pretend to idle for more than 30 seconds before I did that.
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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Seems I was a bit premature, with the onset of cold weather I continue to struggle with the idle on my Honda. My previous repair was not fully understood. It seems that when the engine is completely warmed up it will idle smoothly at 1100 RPM. Previously, I thought this idle was all the time, because during the summer I seldom used the car and usually took it straight to the freeway for longer drives and when I parked it due to the air temperature (the coolant, maybe?) would stay warm. When I fixed it the engine had been running in the summer heat for more than an hour, so it looked really good.

    Now, due to the cold weather, I am taking it for shorter drives or if I leave it parked somewhere for awhile I've noticed the idle is still malfunctioning. The engine will idle at just about 2000 RPM until the engine warms up. Then usually the idle will drop back down to 1100 and hold until I let the engine get cold again. Sometimes though, when I am coming to a stop and the car is out of gear I will see the RPMs rise and fall between 1500 and 2000 rapidly (this only occurs when the car has been driving for awhile, but maybe isn't fully warmed up).

    Please recall that before I replaced the choke opener I pumped line 18 and did not see a drop in RPM. Does this mean that thermovalve A/B? or the fast idle unloader needs to be replaced? I've inspected the tubes very carefully for leaks and am as confident as possible they have not failed, although I could be missing something.

    I'm digging around in old posts and on youtube for answers, but any ideas or locations to look would be very appreciated. Feel free to educate me too. Thanks
    Last edited by Deepdriller; 12-01-2014 at 07:48 PM.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    I will see the RPMs rise and fall between 1500 and 2000 rapidly
    Aside from this, it sounds like the car is behaving normally?
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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    That sounds like a leakng vacuum advance diaphragm or vac hose collapsed or leaking slightley.
    A good spray down with choke cleaner all inside the top hat is a good winter prep though.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Yes and no, the high idle and RPM fluctuations have been a recurring symptom for some time now. The idle problems seem resolved when I replaced the automatic choke opener, but I actually think that was only a partial solution (as the best idle I was able to achieve was a suboptimal 1100).

    I did not mention the noise previously, because I thought it is unrelated and did not want to muddy the waters, but the car has recently started to make a squealing noise (long after the idle problems first surfaced). I am pretty sure it is a belt squeaking. You can hear periodically, not just on startup. It went away for awhile (couple weeks to a month), but has come back again recently. I think it might be the timing belt. Or maybe the water pump? Maybe the distributor? It sounds like the noise is coming from the belt area, but it might be air escaping at high pressure for all I know.

    I intend to have it fixed by a mechanic asap, but would like to delay dropping the car off until I know if I need to replace another part that I cannot access myself (like a thermovalve... still can't figure out where those are located).

    I have video taped the sound (high pitch errrrr sound) and uploaded. I would really appreciate any suggestions, perhaps it is related to the idle after all. Please let me know what you think.



    P.S.

    The car starts excellently and when warmed up after being driven for awhile idles between 850 - 1100. Occasionally, even when warm though the idle will bump up and get stuck at approximately 1500 RPM, but if you goose the throttle the RPM will fall back down to a normal idle.
    Last edited by Deepdriller; 12-07-2014 at 07:38 PM.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Thermovalves A & B are behind and below the carb on the drivers side. You can see them without removing anything on my DX. 'A' is closest to the drivers side.
    The 3 port one is thermovalve A and will have 3 hoses marked 17, 18, 19. !7 is on the end, the vent line, 19 is next, and just a bit further down is 18. I have my doubts that the fast idle unloader and thermovalve could cause the 'bouncing idle' between 1500 & 2000rpm though; Because the fast idle cam requires you to tap the throttle peddle to reset back to the higher RPM. I don't see how it could allow the idle to oscillate up & down like that. ....But the 1500 & 2000 rpm is more than a curious coincidence. ...sorry I have no experience with this one.

    If thermovalve A is causing the high idle to hang, you could try capping (plugging) the line 17 (vent)port on the valve.
    This should allow 18 & 19 to pump down to vac ( releasing the fast idle unloader) regardless of engine temp.

    (then go back to check for vac on 18 & 19 at the fast idle unloader)

    That noise sounds like a bearing going out; maybe water pump or alternator. Take the belt off and you should be able to feel if the bearing is loose or rough.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Thanks for the information. I finally had the opportunity to get back into this project and I think a solution is close!

    Upon locating and inspecting thermovalve A I found that that the line 18 nipple is broken off. The line 18 vacuum tube is not connected, just dangling with the broken nipple still attached (sorry, couldn't manage decent photo). I think this means that line 18 never provides the vacuum needed to engage the automatic choke opener, creating a constant fast idle.

    Apparently, once the engine gets to temperature another system must be activated and engage the automatic choke opener. Is this line 26, line 19 or something else?

    Occasionally when the engine is at temperature the fast idle will return (RPM ~2500), but tapping the throttle will return the idle to 1000 RPM. I read one of POS carbs old posts which said that if line 19 has vacuum it will release the fast idle cam. I suspect this is what is going on.

    I've tried searching, but I cannot figure out the purpose of line 26. The stage 1 vacuum line removal guide (see here: https://www.3geez.com/forum/how/11067...tml#post470501 ) shows it plugged. I am wondering can I simply pipe vacuum from another line and give constant vacuum to the choke?

    I inspected the nipples and vacuum tubes on lines 17 and 19 and they appear intact. I think they are functioning.

    I've attached the image below for easy reference:
    -new-choke-opener-tubes-jpg
    Last edited by Deepdriller; 05-02-2015 at 11:42 PM.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Line 26 is the 'cranking leak solenoid' line. It makes sure your choke stays closed while cranking the engine to start. It goes right to the black box. You can test it's function with a vac gauge. It should hold a vac (to the black box) unless you are cranking the starter.

    If Port 18 nipple is broken on thermovalve A, I would suggest you bypass the thermovalve altogether: just connect 19 and 18 together at this point. Line 17 is the 'vent' line so you can just cap it to avoid getting dirt into the vac system.

    It's summer now so bypassing thermovalve A should be OK. It may take a bit of feathering the gas pedal when you first cold start, but only will be a problem when winter comes.

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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Mine started something very similar not long after I purchased it, cure was simply a good cleaning and before cleaning with cleaner I run a can of sea foam through it and after that cleared I changed the plugs, since every time I fill the tank I put 4 0z of marvel mystery oil in the tank, I've ran with and without and motor is happier with the marvel in the tank, I'm not a snake oil enthusiast but problem did go away

  25. #25
    DX User DanJDT's Avatar
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    Oct 2017
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    1988 Honda Accord
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    Re: Throttle/idle Issues on 1987 Honda Accord LX

    Hey Deepdriller. you still around here?

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