Keep my car running!
April 23, 2012 12:49 PM   Subscribe

Car problem: 1994 Honda Civic suddenly developed rough idle, and stalls out when idling but only after the engine has warmed up. This began on a warm day last week. It had a similar problem last summer but not as bad as it is now. Last year the problem went away after a month or so. Is this something I could fix with a gas additive, or by opening up the idle control screw a bit? Should I wait for it to go away again or just get it in for service? A few more details inside.

The car starts reliably after it has stalled but will continue to run in idle only if I keep my foot on the gas a bit. The air filter looks OK. Coolant temperature is normal, and the check engine light does not come on. It's a gas engine, not diesel. The car burns a fair bit of oil.

I don't have tools or skills for any complicated repair. I can only do fairly simple car stuff. So... any ideas? Thanks in advance for your help.
posted by DarkForest to Travel & Transportation (20 answers total) 2 users marked this as a favorite
 
On these hybrid carbs, sudden behavior changes are often due to something going wrong in the electrical (solenoids / wiring) or vacuum (hoses). It's extremely unlikely that your idle speed screw just suddenly cranked itself a turn after all these years. So the rule here is: start with the simplest to check and work your way toward the black magic end of the trouble list.

Testing vacuum is the easiest first step but requires a vacuum gauge you certainly don't have. :( Testing electrical connections and solenoid activity is next-easiest, but that requires a bit of experience to know what does what. Testing carb guts is a pain in the rear and requires a lot of experience.

Putting a turn or two on the idle speed screw might make the problem go away, but there's a 99% chance it would just be hiding the problem. Considering the pain you may suffer if you've lost a vacuum line or solenoid and it causes the carb to run lean ... well, my advice would be to take it into a shop that knows carburetors of this era. (It's a surprisingly dying art.) They should be able to give you a first-order estimate in just a few minutes.
posted by introp at 1:04 PM on April 23, 2012


(I suppose I should've asked first: you've shot carb cleaner into the throttle body, actuated the linkages while doing so, etc.? That's essentially free. Just read the fire hazard warnings on the carb cleaner can!)
posted by introp at 1:06 PM on April 23, 2012


Get the oxygen sensor checked first. That was my problem. Also, I noticed that I wasn't getting the acceleration or mileage I was used to.
posted by bonobothegreat at 1:27 PM on April 23, 2012 [1 favorite]


I'm with introp and bonobothegreat --- vacuum line blew, or oxygen sensor is contaminated and giving false data. This sounds exactly like an issue my (carbed) 89 Escort had.
posted by Sunburnt at 1:30 PM on April 23, 2012


Where are you from? If this is a US car, it will be injected, not carb, so it could be Mass Air Flow sensor as well as a vacuum leak or gumming up.

I'd be surprised it was an O2 sensor causing a stall. I'm not even sure if they have much sway on the idle circuit (ie I think they are ignored at zero throttle).

Check the vacuum lines (small diameter rubber hoses - about 1/4" OD- coming in or out of the intake manifold). Any cracking, or anything that makes the idle speed change when you wiggle it means a vacuum leak. This is the cheapest likely cause.

Do not mess with the idle speed screw. It isn't something that will fix anything, just push the problem further down the line.

The fact that it does it only when warm suggests it is running lean once it gets off the cold map. This could still be vacuum, MAF sensor or even electrical (weak spark). Too difficult to diagnose at this stage, but don't go buying 02 sensors or any expensive components as it is impossible to say with the information given.

My suggestion:

If you haven't serviced your car recently, I'd change the spark plugs, leads and (if your car even has one) distributor cap and rotor arm. Once that variable (which needs doing regularly anyway) is out of the way, I'd check the vacuum lines then start looking at the MAF sensor.

It is possible that if you start your car with the MAF sensor connected that it will run on a default map. You can try that and if the symptoms are better then it points towards it being this. The MAF sensor is my guess as running lean is classic symptoms - more air is getting past the sensor than it realises and so it doesn't inject enough fuel and the car can stall.
posted by Brockles at 1:42 PM on April 23, 2012


Don't replace the part I'm about to suggest until you've ruled out the other stuff mentioned by others first, as it is expensive.

However, I knew folks with similar-vintage Civics who had problems with rough running/dead engines, only when the engine was warm, and the problems were ultimately traced to the electronic distributor. A pricey part, and prone to heat-related trouble.

Again, don't follow this lead until you've ruled out the cheap stuff.
posted by davejay at 2:38 PM on April 23, 2012


I think one of your cylinders isn't firing for at least some of the time when it's running rough.

That cylinder probably has a weak spark due to a poor connection that gets worse when things expand as the engine compartment warms up, so I would replace the spark plug wires-- and the plugs, because at least some of them are likely to be fouled with oil since you are burning oil.

But I would check the oil level in your transmission before doing anything else if your car is a standard, because I had a Civic standard of about that vintage which started missing toward the end of long drives, and the problem turned out to be a dry transmission (there was a crack in the casing) which would overheat on long drives, then the spark plug wire that came closest to the transmission would cook in the heat, loosen up on the plug and start failing to transmit the spark properly.
posted by jamjam at 3:17 PM on April 23, 2012


It's your timing belt. Just adjust the idle and this should fix your problem. :)
posted by brittaincrowe at 3:59 PM on April 23, 2012


Some of the advice above is puzzling to me, and/or contradictory. Given your lack of mechanical skills/knowledge, I would suggest that you take it to a mechanic, preferably one you have used before, or one that you or a friend trust.

By all means have a look around the engine bay, check the hoses to see if any are perished/cracked/leaking, etc, but if you adjust anything, be sure you know how to reset it in case it makes things worse.
posted by GeeEmm at 4:04 PM on April 23, 2012


Response by poster: Thanks for your answers so far.

It's an American car, though manufactured by Honda Canada.

I checked the hoses and didn't notice any obvious problems. But I'm sure that I could have missed something.

My initial thought was that it was a fouled plug since it does use a lot of oil and I think my shop one time told me that the head gasket was probably bad. I should probably check if it's easy enough for me to pull the plugs and check.

I'm hoping to not spend a lot as the car will probably succumb to rust in the next year or so. It would be nice to get another year out of it though. Generally its been very reliable and still gets great mileage.
posted by DarkForest at 4:27 PM on April 23, 2012


Response by poster: Oh, also, it idles rough even if I give it gas and rev it up. I should have mentioned that in my original question.
posted by DarkForest at 4:31 PM on April 23, 2012


When is the last time the fuel filter was replaced? Could also been the pump and/or tank screen.
posted by narcoleptic at 4:42 PM on April 23, 2012


Yea, what brockles said (he is usually right imho on most of these threads). The blown head gasket alone could explain all your problems and if so your car is probably done. I think the oil burning has caused you more serious problems. This and that it runs rough when warmed up make me think it is a bad sensor, bad ignition system component or emissions systems. BTW all these systems are HIGHLY interrelated. You could have a gummed up Exhaust Gas Re-circulation system which isn't opening up the valve when it should. With Honda engines, in general, but the VTEC engines in particular are somewhat prone to carboning up the EGR valve and system. The H series are really bad at this. You have a D or maybe B series engine depending on the actual model of civic you drive. The plugs could be fouled with all the carbon from burning oil, It could also be the O2 sensor (and they aren't really expensive on these cars-usually about 40$ for just the part). And the list just continues to go on and on. You need to take it to a mechanic to get it looked at and possibly put out to pasture if the car is rusting away anyway.
posted by bartonlong at 4:47 PM on April 23, 2012


1) Brockles is right. The o2 sensor does have some input into the idle, but only in a round about kind of way. If you are getting great gas mileage, it probably isn't the o2 sensor.

2) If you were advised that you have a possibly had head gasket, this could very well cause this problem. If you don't want to spend to fix it, just keep the oil and water topped up and drive it until it dies.

3) "It's your timing belt. Just adjust the idle and this should fix your problem. :)" There are two different kinds of timing in a car. The timing belt, which either works or it doesn't, and the ignition timing, which is adjustable. However, on fuel injected cars, it shouldn't really ever need to be changed as the computer has ultimate control over the timing, and will adjust it dynamically. These are all mechanical relationships to each other, and x degrees before top dead center shouldn't be changing much over time. If it is ignition related, it's a bad cap and rotor, bad plugs or bad wires. That should cost you all of $40 at Autozone.

(OK, it's possible for an old timing belt to jump teeth, but that's probably not likely as the car would probably run terribly in all situations, not just at idle after it is warmed up.)

4) It could be a lot of the various sensors, but I would not bother with just changing them willy nilly unless you are getting a specific code, or can check the sensor with a multimeter. I would guess, if it is going to be a sensor, it would be something like a coolant temperature sensor, an air intake temperature sensor or a map sensor. But again, you probably would have noticed poor mileage before any idle problems appeared.
posted by gjc at 5:29 PM on April 23, 2012


DarkForest: "My initial thought was that it was a fouled plug since it does use a lot of oil and I think my shop one time told me that the head gasket was probably bad"

If these are true and you only want to get another year out of it, change the spark plug as needed and keep adding oil. If a new plug (and you don't need to replace the whole lot, just the one that is fouled) solves the problem, anything else is just throwing money away.
posted by dg at 8:12 PM on April 23, 2012


If a new plug (and you don't need to replace the whole lot, just the one that is fouled) solves the problem, anything else is just throwing money away.

Don't throw it away, clean it and put it back ... and you are not spending any money lol ;-)
posted by GeeEmm at 8:22 PM on April 23, 2012


Stalls while idling, remedied by giving it a little throttle?
Only stalls while idling after it has warmed up?
Irregular idle?
Happens more in summer (warm weather) than in winter (cold weather)?

These are classic symptoms of an Idle Air Control Valve getting fouled, and not being able to operate properly to maintain your idle (when your throttle is closed). Locate, remove, clean, and re-install your Idle Air Control Valve on your Fuel Injected Honda. You can get a can of stuff just for this purpose down at the local useless auto store.

It's cheap, and one of the joys of a geriatric automobile.
posted by the Real Dan at 11:55 PM on April 23, 2012


I think Honda used MAP sensors rather than MAF sensors in these, and MAP sensors are reliable as heck. I'd definitely look at the idle air control valve. Remove the IACV, SOAK it with carb cleaner, swish it around in there, air dry and reinstall.

This link should show you what it looks like. It'll be somewhere on the air intake path.

One more thing: Look at the throttle body. Open and close the throttle. You should hear a distinct clicking. If it's anything like european stuff of that era, there's a switch (maybe a potentiometer) right on there. That's what's telling the car that you're at idle. The IACV's job is to give the car enough air to let it idle when you've got your foot off the gas and the throttle plate is closed. It knows the car is at idle because of that switch. If it's not functioning, the IACV may not do its job right. Check that it's functioning with a multimeter, clean the contacts with electrical parts cleaner. I'm sure you can find a writeup somewhere on one of the honda forums that tells you what to look for.

Oh, I suppose you could also try just unplugging the throttle position sensor while the car is running and check to see if the idle immediately changes. It should, though I suspect the idle will go up rather than down....
posted by pjaust at 5:30 AM on April 24, 2012


Response by poster: Thanks so much for your help. I'll be checking/replacing the plugs and wires, etc. I'll post back when I get it solved.
posted by DarkForest at 7:37 AM on April 25, 2012


Response by poster: Update:

Replacing the plugs/wires fixed the stalling problem. Probably the plugs as the terminals were pretty eroded.

However it was still running rough. I took it to my shop and they said compression was bad in 1 cylinder. Sadly, that won't be getting fixed.
posted by DarkForest at 10:09 AM on May 24, 2012


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