Code 43... running very rich and misfiring at idle

Alright, I’ve searched high and low here and on honda-tech for a solution to this problem.

I’ll cut to the case. The car is a 91 GS, completely stock except for an exhaust. It’s running VERY rich, black soot all over the rear bumper. The other night on the highway it threw a code 43, Fuel Supply System. Once I turned the ignition off and back on it went away. The car audibly misfires at idle and slightly above, and also wants to die or idle really low sometimes at stop lights and such… the idle will drop almost to where the motor will die, then it will either die or stumble a bit and catch itself and jump back up… then back down, then up, down… you get the point. The car runs great other than this idle problem, but it’s definetly running rich.

I’ve been troubleshooting this for a few days now… here’s what I’ve done so far, with no results:

Thoroughly cleaned IAC valve with carb and choke cleaner.
Checked/cleaned the fast idle valve (the plastic piece was snug in there, not loose)
Sprayed all the vacuum lines/fittings with carb and choke cleaner hoping to find a vacuum leak (none that I can find)
Checked timing… dead on 17 degrees
Replaced O2 sensor with brand new OEM
Changed plugs, wires, rotor, cap - new NGK’s gapped at 0.040, oem plug wires, cap, rotor, etc. Old plugs were BLACK, but dry.
Did compression test - 175, 170, 175, 175 - good results
Replaced MAP sensor with a spare I had laying around

What else could the problem be? I’ve reset the ECU multiple times after doing this work. I’m stumped right now, and it’s starting to make me want to get rid of this damn thing, and I just bought it! Anybody have any ideas?

Tell me what Code 43 means.

Fuel Supply System.

I’ve seen this code before on my previous car (95 Civic). In that case, it would sometimes pop the CEL on while I was driving down the highway (just like it did with this car). The problem on my old civic was due to a vacuum leak right at the MAP sensor (forgot to put the O-ring on when I put it back together). It ran in the same manner… very rich and with lots of misfires, fouled plugs a lot and fouled the O2 sensor a lot as well.

Given my previous experience, I immediately started looking for vacuum leaks and moved next to just replacing the MAP sensor with a known good one, but it didn’t fix.

Could this be the “igniter” or “control module” (as the parts store calls it) inside the distributor going bad? This problem seems to be getting worse and worse over the last few days, now when it’s cold it won’t idle at all without constant throttle, and it sounds very lumpy and is constantly misfiring or not firing at all.

Alright, so just for the hell of it, I disconnected the O2 sensor completely this evening and drove around a bunch. The car did not throw any immediate codes, I drove it around a bunch and it acts exactly the same with the O2 sensor disconnected. I’m going to go to the honda dealership tomorrow and see if I can find an OEM denso replacement that will fit my manifold, since the one that’s in there now is a new Bosch universal “cut and crimp” type replacement, which I’ve heard bad things about.

I’ll post again tomorrow most likely. I see a couple other people are having this problem, based on the list of threads in here.

mine keeps throwing the same code and just like you i have a 2 week old bosch o2 sensor and i have checked for every possible vacuum leak and cleaned out my fitv and my iacv with no luck. ill wait for your findings. good luck. thanks, harry

Fuel Pressure?

Well, it could be, what’s the simplest way to tell if the fuel pressure is too high? I don’t think it’s too low, due to the fact that the car runs rich, but I’m open to any and all suggestions right now. I have a good steady flow if I crack one of the banjo nuts on the filter while the pump is on… but that’s the extent of the fuel pressure checks I’ve done (other than replacing the filter itself).

It’s most likely your O2 sensor. If you do some searching on it, you’ll see that fixes it for most people.

Do you throw the code when you “engine brake” ?

Or are you driving around, getting weird hesitations all over the place when your car is fully warmed up, it finally throws a CEL, and it smooths out the hesitation…?

Have you replaced the fuel filter recently?

No codes when I engine brake or accelerate. The code has only come on once after driving for an extended period on the highway (though it did come on while engine braking on a long downhill portion). What I did was pull over right away, shut the car off, then I pulled up the carpet on the pass. side and checked the code on the ECU and got 43. Once I turned the car back on, no more CEL though the ECU blinked the 43 code until I reset it the first time.

The car idles VERY rough when it’s cold, like it’s only firing on some cylinders, and when it’s warmed up finally it requires constant attention with the throttle at stop lights to keep it from dying. Sometimes though, instead of wanting to die, it idles at like 1200 RPM, and you can hear the misfires then very well, even when it’s warm. The rear bumper is covered in soot, and if I park the vehicle and rev it up, it will leave a long black trail of soot behind the muffler. Since the CEL has only come on once, I can’t comment on whether the problem got better when the CEL was on. However, I disconnected the O2 sensor last night (it’s still disconnected infact) and got NO CEL at all, and it still acts the same, no change in the funny behavior and whatnot.

I went to the honda dealership here and inquired about ordering an OEM O2 sensor for it instead of the brand new Bosch I just put in, but they want 196 bucks. Outrageous price, when I can order a Denso OEM one online for 40 bucks from

I’ve already replaced the fuel filter just recently right after I bought the car.

Well, now this morning driving to work, I got multiple CEL’s, all seemed to be when I was engine braking. I still have the O2 disconnected, which is probably the culprit, but tonight I’m going to clean up the old O2 and put it back in (it’s a Denso instead of the Bosch one I have in there). Don’t know where to look next if that doesn’t work. I’m out of ideas and ready to drive this damn thing into a lake.

Does anyone have any code 43 success stories? What caused it and how did you fix it? I’m grasping at straws, but maybe it would help those of us who are having this trouble do some troubleshooting.

Alright, I’m leaing towards the injectors being the culprit. I have perfect fuel pressure and have tried two of my O2 sensors, and one from a friend’s car that runs fine, and still nothing. I’m going to run a can of seafoam through the car (1/3 gas tank, 1/3 TB and 1/3 crankcase), then run it and change out the oil. I will post up my results.

I guess if it doesn’t my next step is to take the fuel rail off and inspect/clean the injectors and replace all the seals. Not too hard, just have to figure out how I’m going to clean the injectors but I"m sure I’ll find some info by searching here or honda-tech.

I have had a code 43 issue ever since i got my teg. Since then i have changed o2 sensor (fram), plugs, wires, complete distributor (coil and igniter), cap, rotor, cleaned the IACV multiple times. My CEL only comes on when the car is at idle. It used to come on quite frequently at idle, but after the o2 sensor change, it only comes on once in a while (not even half as much as before). So the o2 sensor did help, but the problem is still there. I get very unconsistant fuel millage, but it’s never good. Car always has power (well, as much as the 14 year old motor has), and you can always smell un burnt carbon at the rear of the car. Fuel pressure is good. I really think the car is fireing properly, but for some reason it’s getting too much gas injected. My next thing is the injectors. Please keep us all up to date if the injectors fix your supper annoying problem NotMatt.

hey whichone! tell us about your stuff too, i seem to have quite the same problem! i dont know if this is normal but when i let my car warm up (its winter here, snow all over the place) i can see some brownish dots on the snow (alot of them) and they do seem to come out from the exhaust. would that be unburnt fuel? because it doesnt really smell like fuel but once in a while when i start my engine i can smell a bit of gas from inside.

For how much everyone raves about Seafoam, it sure is a useless product. I ran a can through today… half through the IM (funnelled it into the brake booster hose) and half in the tank with a little less than 10 bucks worth of gas in there. Lots of smoke, and no change in performance or the crappy idle at all.

Guess it’s time to pull the fuel injectors out tomorrow and see what they look like.

after you suck it in you turn the car off and let the stuff sit in the cylinders and soak into all the carbon and what not… you can also pull plugs and put it directly in…

I know how to use the stuff… what I’m saying is it did nothing for me on my Integra, and also did nothing for me on another vehicle I tried it on that had similar problems.

The fuel injectors are coming out tonight, I’m going to clean them and re-install with new seals and see what happens.

Also, another note… there’s another thread on the front page about idle problems, and I’d like to mention again that I have searched this problem over and over and have tried everything in the “Idle troubleshooting” teg tips article except for replacing the ECU. If cleaning the injectors does not fix the problem, my next step is to replace the IACV, since it might be bad even though I cleaned it.

viZion, i dont have anything else to add, my story is all there. I live in quebec too :clap:
NoMatt, please keep us up to date about the injector cleaning/swap and good luck.

Any update? :hmm:

Yeah, my injectors were filthy. However, cleaning them did not solve the problem. I suppose I might not have got them completely clean…

I seriously thought I had found the culprit when I took that first injector out. The tip was COVERED in carbon buildup (lotta good that can of Seafoam I ran through there did). I pulled all the injectors, cleaned off the big carbon stuff, let the tips soak in some carb/choke cleaner, then I pulled all the old seals off of them (o-ring and rubber seal at the top), scraped some of the (now soft) carbon buildup off, wiped them down good. Then I took the small filter out of the top and filled it’s place with carb/choke cleaner and used a 9 volt battery to click the injector a few times so the cleaner would make it’s way through. I soaked the filters as well. Next I scraped some of the carbon buildup off the inner part of the manifold where the injectors go, installed new seals at the manifold and bolted everything back together.

Disappointing results… the car felt better that night, it wasn’t dropping the revs close to dying at idle, but it still misfired. Now that I’ve driven it around for a few days and made a long trip with the car, I’ve come to the conclusion that the whole process did nothing. The car still amost dies when I let off the throttle in neutral, it still misfires at idle and slightly higher, and it still runs like complete dog-poo when it’s cold.

I’m out of ideas. I have a bid in on a new IACV on eBay, maybe mine is bad despite my cleaning it.