Hey guys, I recently scooped a non-running 00’ EX and have been fiddling with it for a few days. I got it running but now I’m trying to sort out a misfire.

The car sat for about 2 years, and was told he quit driving it on the count of it leaking coolant. When I got it home the first thing I did was completely drain the fuel and put some fresh in. It didn’t have any spark, and the entire ignition system was in bad shape, very worn plugs and what appeared to be the original cap/rotor. So, It got some new NGK iridiums, NGK wires, distributor cap, rotor, and a new coil. It fired right up. I soon found the coolant leak, a small tear in the heater hose on the side of the head right after the fitting 😏. All seems well except for the misfire codes and rough idling when the engine is cold.

When the car is first started and the revs are about 1500-1800 it runs perfectly smooth, but after about 10 seconds when the idle starts to come down, the misfiring starts. All cylinders, random misfiring. When it completely warms up, the misfiring almost completely stops. If you shut it down at anytime during warmup and then restart it it again does the same thing, about 10 seconds of smooth running, then back to the misfiring. Compression test showed great results, 185,179,186,193. At WOT the car runs great, and driving down the road cruising is fine. This only seems to be occurring at no load/idle conditions.

 

Check the ignition timing at idle and at 2000 rpm, compare to OE.
Also check for vacuum leaks, vacuum gauges are pretty cheap at Oriellys or Advance.

 

Check your distributor coil. I had an original Honda coil on my car. It failed at about 340k miles. I would get misses at low rpms, like when stopped at a light. Eventually the car wouldn't start up anymore. The coil spark was shorting to ground through its black plastic case. I replaced the coil, but one of my Honda friends says, in an emergency, just wrap the entire plastic case with a few layers of electrical tape. Try that and if that makes the problem go away, you know you have a bad coil.

 

I’ll have to get a new timing light to check base timing but with my scan tool hooked up it is reading about 27 degrees at idle, not sure sure how the base timing would correlate with the factory timing map at idle… that’s all I can check on that for now, I have been meaning to get a new gun anyways so I’ll probably grab one this weekend and report back on that.

I have replaced the coil, twice now because the first one I got which was a WVE brand, actually was slightly deformed in a way that bound up with the distributor cap, I suspected at first that this was somehow causing a bad gap somewhere leading to the misfires so I actually got another new coil, this time an NGK brand and it fit perfectly in the housing but sadly it had no effect on the misfire and continued to run the exact same

 

Okay, I was not yet able to make it out to get a new timing light but after looking at a d16y8 ignition map and comparing with the live data on my scan tool it appears to be running the correct timing. Unless adjusting the base timing affects this underneath then I would assume ignition timing is ok?

what is not yet happening during the first 5-10 seconds of startup? I remember reading something about 15 years ago about how the oxygen sensors are not in use during the initial startup… I feel like whatever is causing this issue has to do with something that’s not yet “active” during the first few moments after startup. Could it potentially be a bad TPS? IAC? I did notice on one occurrence that right at about 10 seconds after startup when it started to misfire, I gradually applied throttle to maybe 5% or so to see if it had any affect on the misfire and the rpms actually fell from ~1500 rpm to about 500rpm and the engine ran very rough and the tone deepened, as if loading up on fuel. But as soon as the throttle was pushed beyond that threshold or let off it returned to the normal random misfiring. I haven’t tried again to reproduce that on this civic again but have ran into it before on cars with oxygen sensor codes, although they were actually throwing codes for oxygen sensors/ cat efficiency…

 

Bumping this up, hoping someone else can chime in on these misfires

 

Like always, I would say invest in a $20 multimeter (such a handy little important device..) and definitely test that tps sensor, very easy to do.. it could be the problem. I think it would be running in open loop and not reading any other sensor other than throttle position until it has reached a certain temperature.
If it checks out ok, I would disconnect, clean every ground to bare metal (battery too) in the engine bay and make sure it's on snug. Maybe check inside the distributor for arching and also check the spark plugs color. They white, tan, black? Is it running too lean/just right/rich? Is the motor completely stock? Try just a basic replacement spark plug instead of going fancy. Just some odd things to check/do.
Start narrowing it down.
Using the multimeter will save you a lot of money and guessing. If your one of those people that just throws parts at it crossing your fingers, don't .. you can test every sensor.

 

I do have a multimeter and will give the tps a voltage check as soon as I get around to building a test harness for it with a plug from an old parts engine harness, I just feel it will be cleaner then trying to probe around with alligator clips or cutting into the wire insulation and it will be a nifty tool to keep around. That being said, with the scan tool hooked up it reads 9.8% absolute throttle at idle and 92.5% at WOT but does have a smooth curve with no dead or jerky spots… Short term fuel trim at idle is around 6-9% also. my 00 crv reads similar numbers and it runs fine. I was able to get someone to rev the car while I stood back and it is running rich as I’m getting a decent sized puff of black smoke when revved to anything over 4-5K … This car is 100% completely stock. Not one single mod, period. The inside of the distributor looks good, no signs of arcing. I plan to clean all my grounds next, the chassis is clean with no rust and the electrical connections look very good considering age but I still do plan to give them all a good clean. It’s weird because if I give the car some revs or drive off right away, it runs awesome and as soon as it’s warm it’s great. It’s just annoying in that I know something is happening that shouldn’t be, and now I know it’s definitely getting too much fuel.

 

does this engine have an Idle Air Control valve? If so clean that also, a dirty crunchy one can cause a lean missfire

 

Okay, after looking a little closer I noticed that the PCV hose was collapsed right where it connects to the intake manifold, completely suffocated. I replaced the hose and changed out the PCV valve which was the original unit. I also replaced the PCV grommet but sadly pushed half of the old grommet inside the breather while trying to extract it, luckily it seems sorta stuck in the baffling where it sits in there so I won’t worry about it just yet, but will extract it in time. I was feeling good that the PCV system being inoperable was responsible for the misfire, but when I fired it up there was no change whatsoever. I then decided to have a look at the IACV. When I pulled it back I saw the screen was completely gunked up, to the point that I couldn’t see how any air could pass through it. I cleaned it throughly and again felt confident this could sort the misfire, but again, no change whatsoever.

 

Ok, so after finally getting some more time to actually drive the car I have observed the following. This is not just happening when it’s warming up, it is occurring all the time, but still in strange ways. When the car is fully warmed up it will still randomly misfire with one little “pop” from the exhaust note and a visible drop in rpm every 1-5 seconds, it is not consistent. IF you run any kind of load to the engine at all, be it a/c, headlights, etc, it will not misfire at all. If the engine is revved to around 2K and held there, it will misfire. If you shut the car off and restart it where it revs around 2K for a few seconds on fast idle, it will not misfire. During cruising I am noticing some slight hesitation, as in I can feel the engine running rich/lean and loosing some power, and randomly snapping back at higher throttle positions, not really like it’s misfiring, but just not running stoich.. there is still the heavy black smoke clouds when ran hard. When using the live data on my scan tool the long term fuel trim is only 7%… short term fuel trims are right around 7% at idle but never more then 12-15% when cruising, O2 sensor reading has a perfect wave between .1 - .9v .. even though to me the problem feels to be worse, it’s now not even triggering a CEL. Which used to always be random misfire, with codes for every other cylinder individually.

 

I am having the exact same issue!!! I bought my civic that had been sitting for 5 years and I have done very similar to you, I haven’t found any info online about this issue because it’s so spontaneous. Mine is showing the exact same issues. I’m starting to think it’s distributor related but as you said it didn’t change yours. I will update if I find anything…

 

well it sucks someone else is having to troubleshoot the same problem as me but it’s nice to know there’s two of us working on solving it at least. I hope it winds up being the same issue for both of us lol. I just did a valve adjustment today and many of mine were between .003-.004 too loose. It sounds better but it’s still got the hiccups…

I thought about swapping the ignitor but I’m keeping that as a last resort, my OEM coil was toast though and it does seem that they can affect each other when they aren’t operating smoothly. I have been back and forth on this but at this point I’m leaning towards a fuel issue, I’m just not sure why it runs perfect at WOT. I’m hoping someone can chime in who has a better understanding of exactly how specific sensors can affect ECU outputs then I do or someone who has experienced the same problem and solved it. I’m going to be very diligent in checking for vacuum leaks next time I’m over the car, I’m just trying to get my head around how it could run smooth during fast idle but not when the revs are manipulated by the throttle.. if it were a vacuum leak I feel it would just run like **** regardless

 

I have been trying to troubleshoot more today

What I’ve done:
- Drain and fill up tank
- Replace fuel filter
- Compression test (good)
- Air filter
- Pulled dizzy and cleaned everything (couldn’t see arking spots anywhere)
- Blocked PCV valve
- Cleaned IACV and throttle body
- Oil and filter change
- Replaced headers (originals were cracked, makes me think it may be my O2 sensor??)

Things I need to check and/or change that could be my issue:
- TPS, MAP voltage
- New dizzy
- Fuel pressure regulator, fuel pump?
- Injectors
- O2 sensor

And if no success after that, I’m stumped!

 

I have more or less done the exact things as you with the exception of the exhaust manifold as mine is ok. I’ve got a very similar to-do list as well… I will update accordingly

 

Unfortunately my issue just got worse recently, had it idling (wasn’t misfiring bad at all) and I turned it off and went to start it and it cranked but didn’t start, after about 3 tries with my foot to the floor it started and wasn’t happy at all. This made me think it was the ICM. I also cleaned my O2 sensor today, nothing…

 

I feel like I’m on to something here but I’m not certain. I decided to drive the car to work this morning and this is the first time I’ve had it out in the dark. When I turned the headlights on I noticed they were flickering, when I turned the a/c on the flickering stopped. When I got home I got out the multimeter and performed some voltage tests. With the engine at idle and no loads I was reading between 14.8-15.6 V .. with the a/c only it drops to around 13.0V.. when I have both a/c and headlights it comes up to about 14.0 v … so it appears to be overcharging when there are no loads, or not enough loads… I’m wondering if this drop in voltage when I’m engaging my a/c is what’s smoothing out my idle? Could the extra volt be enough to throw off an injector pulse and cause a rich condition? I want to replace the alternator but hate to get a shitty aftermarket one… there’s a shop around here that rebuilds alternators and starters, I’m assuming they can sort out one that’s overcharging.. I’ll have to call

 

Hmmm.. sounds like you may be onto it, after reading your reply I went and tried the same thing with mine. Unfortunately mine was perfect, 14.4V with no load and 14.27V with lights and a/c on. I think my issue is distributor related or fuel related 🫤

 

Did some of you find the root cause for random misfires?