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My 1984 Honda Accord idles poorly (between 200 and 300 RPM) once the engine is warmed up. This causes the vehicle to shudder excessively when stopped at a red light. This only happens when it’s cool outside (<70F) or when the car has been running for a while (30+ mins) and even then, only intermittently. I can feel it go away as soon as I press even lightly on the gas pedal. Normal idle is about 800 RPM.
I have a feeling that it's fuel-related, as the car is sometimes difficult to start on cool mornings. I replaced the fuel pump a month ago to fix a stalling issue, which it did. Fuel filters and air filter are new, spark plugs and wires are only a few months old, distributor and all related parts are also fairly new. I can also smell either raw fuel or exhaust fumes when I have the window down in traffic (I used to think it was from traffic in front of me, but I smell it even when there are no other cars nearby). That makes me suspect a possible fault somewhere in the EVAP system or purge canister, but I don't know for certain. No vacuum leaks. The car passed emissions testing back in March. New timing belt & tensioner as well, if that's relevant.
This car is carbureted (carb was rebuilt back in June) and is too old for any sort of TPS/CPS/MAP/MAF equipment. It's also too old to have a check engine light. This makes diagnosing problems like this a bit of a PITA....
I feel like the rough idle is related to another intermittent problem - sometimes while accelerating coming out of a turn, it seems to badly misfire (feels like the transmission is harshly downshifting) but then it's fine after that. Even then, it only does that about 1/5 of the time. But it's bad enough to literally pull you forward in the driver's seat for just a moment, like the engine is bucking. These problems aren't new - they've been on/off ever since I bought the car back in January. The only things I haven't gone through since that time that could possibly be the culprit would be the EVAP system, O2 sensor (replaced in 2010 according to receipt from PO), and catalytic converter (deemed "OK condition" by mechanic). I've noticed a slight decrease in MPG recently as well.
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It’s been a long time since I messed around with a carb, but have you checked the choke kick down? It seems like it is running very rich from what you describe.
I would check the carb float and needle. It’s possible that the fuel level in the float bowl is a bit too high, allowing some raw fuel to flood into the venturi.
That could explain the poor idle and fuel odor, and why the condition clears up with a bit of throttle.
Thank you both for your replies. I drove the car around again today and the shaking/rough idle is especially pronounced when I’m slowing down/stopped facing downhill. I checked the fuel bowl level through the fuel bowl “window” and it looked to be right where it should be, in the middle. I feel like I should also mention that the problem also disappears if you switch from Drive to Park mode (goes back up to 800 RPM), I do this in drive-thrus and long red lights. But put it back in drive, and the RPMs will drop way down to 200-300 and shake again until you accelerate.
I’m thinking about driving the car around until it warms up and begins to idle poorly, then parking it in front of my house and taking off the air cleaner cover to check the carb while it’s running. Maybe have someone throw it back in drive with their foot on the brake while I look at it to see what it does.
Well the car is definitely running rich, and is still hard to start when cold outside. Again, the warmer it is outside – the better the car runs.
What makes it difficult for me to believe that it could be the carburetor is that not only was it rebuilt back in June (and checked twice since then for free under warranty), but also: when driving the car for more than 30 minutes even when warm outside, the car will begin to randomly shudder when stopped at a red light as well, not just when cold. However, unlike when it’s cold outside – the problem will actually correct itself after about 5-15 seconds of sitting at the red light….the RPM will magically move back up to 800 where it should be and the shuddering stops completely, smooth as can be. And if you sit there long, it will do it again about 30 seconds later. And so on and so fourth. These symptoms, and my car in general, have been very sensitive to outside air temperature ever since I bought the car nearly a year ago.
These symptoms are not consistent with a carburetor problem, although yes it is fuel-related. I’m thinking that the only sort of thing that could magically correct itself every few seconds under specific outdoor air temperature conditions like that MUST be sensor-related. This afternoon I was browsing through my Accord’s parts available on rockauto, just aimlessly clicking through menus out of boredom. Then I came upon this – Air Charge Temperature Sensor. I completely forgot my car even had this thing. Somehow I had kept overlooking it over the last few months. It sits in the air cleaner assembly on top of the carb.
Look at the symptoms of a Air Charge Temperature Sensor gone bad. Those sound exactly, play-by-play what my car has been experiencing for a long time, to the point where I just began to assume that’s how carbureted cars are supposed to run. But since the part is $70, I want to be absolutely sure that I’m not just throwing parts at the problem hoping that will fix it. What do you guys think?
Should be easy to test the sensor.
Watch this video, but where he is testing the sensor, he keeps saying voltage when he means resistance.
https://www.youtube.com/watch?v=N5FGh8T4qmE
This page has a table of values by temperature, not sure how accurate it is for your application.
Your egr valve has a carbon build up. Remove it, clean it make.aure.the rod moves in and out easily, then check it for a vacuum leak. If it’s good.after all that, reinstall it. Make.sure the tube for it is also clear enough. Much newer civics have a weird chamber leading to the egr that is long and against the head, that sometimes has to be removed and cleaned, but not sure if your accord has that.
But seriously, it’s the egr valve. This was a common thing on cars from the 80’s and early 90’s. The symptoms were exactly the same as what you described.[quote=”peshewa” post=177644]Your egr valve has a carbon build up. Remove it, clean it make.aure.the rod moves in and out easily, then check it for a vacuum leak. If it’s good.after all that, reinstall it. Make.sure the tube for it is also clear enough. Much newer civics have a weird chamber leading to the egr that is long and against the head, that sometimes has to be removed and cleaned, but not sure if your accord has that.
But seriously, it’s the egr valve. This was a common thing on cars from the 80’s and early 90’s. The symptoms were exactly the same as what you described.[/quote]Pulled the EGR earlier this afternoon:
It didn’t seem too bad, I scraped a bunch of the carbon off with my key. It held vacuum perfectly fine, the rod moves in and out easily.
Here was inside the EGR mount:
Couldn’t really get in there (Honda decided to place a massive vacuum line hub literally right on top of the EGR valve), so I wanted to get your opinion before moving forward with anything around there.
My service manual vaguely mentions a air charge temperature sensor, but doesn’t really specify exactly what it looks like (Rockauto shows it differently too) but there is this strange thing inside the air intake, that is never even shown in the manual at all:
On the underside of it, there is a harness.
I tested the above harness using the video dtidman posted earlier. The harness has continuity, but resistance repeatedly clocked in at 00.1-00.2 (I did the rest several times and tried different ground points to be sure), instead of the recommended 05.0 range.. So the harness is not getting (enough) power? I tried to trace the wires but they get lost in a bunch of plastic tubing that lead to either the control box (this car’s version of an ECM) or the fuse box. I’m gonna have to rip that tubing apart if I want to check the integrity of the wiring.
Plus there’s still the confusion over exactly what part(s) is the air intake/charge temperature sensor on this car. Rockauto and Carid show this as being it:
But there’s two of them, and my service manual shows those as being Air Bleed Valves.
(continued)
Meanwhile, the manual vaguely acknowledges the existence of a specific air intake charge temperature sensor…
Neither the manual nor car parts websites show or mention the weird thing with the harness that I’m seeing at all. What do you think?
[quote=”Temeku” post=177739]I tested the above harness using the video dtidman posted earlier. The harness has continuity, but resistance repeatedly clocked in at 00.1-00.2 (I did the rest several times and tried different ground points to be sure), instead of the recommended 05.0 range.. So the harness is not getting (enough) power? I tried to trace the wires but they get lost in a bunch of plastic tubing that lead to either the control box (this car’s version of an ECM) or the fuse box. I’m gonna have to rip that tubing apart if I want to check the integrity of the wiring.
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Could elaborate on what you did here? Are you testing the resistance on the harness or the sensor? What points were you measuring?
[quote=”dtidman” post=177809][quote=”Temeku” post=177739]I tested the above harness using the video dtidman posted earlier. The harness has continuity, but resistance repeatedly clocked in at 00.1-00.2 (I did the rest several times and tried different ground points to be sure), instead of the recommended 05.0 range.. So the harness is not getting (enough) power? I tried to trace the wires but they get lost in a bunch of plastic tubing that lead to either the control box (this car’s version of an ECM) or the fuse box. I’m gonna have to rip that tubing apart if I want to check the integrity of the wiring.
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Could elaborate on what you did here? Are you testing the resistance on the harness or the sensor? What points were you measuring?[/quote]
I tested the resistance of the harness using the method shown in the video you posted.
I tested both of the highlighted connections. Same result, 00.1-00.2. And yes I made sure I was doing it correctly, using the right calibration on my multimeter (I even tried multiple others just to see if it made any difference) and the ignition turned to the “ON” position.
The car seems to be idleing a little worse now within the first two minutes of starting, then drives like normal. Not sure why.
Hopefully you fixed the problem by now but here’s my experience with something close to yours.
First of all, that idle speed is probably way too low. I think the lowest idle speed I have seen is 700 rpms on my boat motor.
The last carbed car I had was my toy 67 Mustang. It developed a rough idle and it would die at idle unless I kept it up at about 1500 rpms. It usually idled around 900-1000 rpms. I had a vacuum gauge mounted inside of the engine compartment and vacuum at idle was good, even with a mild performance hydraulic cam. If I remember correctly, it was about 12-14 lbs which was enough for the brake booster. I used the “spray and pray” method to look for vacuum leaks in the usual places around the intake manifold and the carb but found none. This problem persisted for a few months until I saw a post on another forum about vacuum leaks that are so minute that it would not show up on the vacuum gauge or the “spray and pray” method. It involved the the throttle plate bushings at the base of the carb. There were actually kits to rebuild those bushing seats on the Holley carb but due to the cost, I just plunked down the green stuff and got a brand new 4 barrel Holley which cured the problem.
This may not be your problem but it sure looks like you’ve covered all the other usual suspects. Good luck.
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