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How exactly do I go about doing that?

 
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https://www.civicforums.com/forums/1...-pcm-idle.html
https://www.civicforums.com/forums/1...-question.html

 
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Thank you.

I had to do a few errands today and I got a couple of mildly rough idles while at stoplights, both times they cleared up by the next time I stopped(in both cases this was not far at all), which is different from prior behavior(where it would idle rough at multiple stops before clearing up).

I will report again after work tonight when I should have had more extensive running(135 miles with regular stops).

I skipped the MAF sensor replacement since everything I saw since cleaning it pointed to the O2 sensor, but that'll be my next step if things don't clear up. It's worth noting that prior to this point, everything I did had some small but definite impact on reducing the severity of the issue - the spark plugs decreased the frequency of the issues, replacing the air filters reduced it further, and cleaning the MAF sensor nearly eliminated the near-stall levels of rough idle. Early signs are good for the O2 sensor reducing things further, but still uncertain of it completely solving the issue.

 
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Okay, so... I had two rough idles. Both very early on in the route, both only SLIGHTLY within the range that would make me worry, and both cleared up after very little further driving.

I am not willing to say the problem is FIXED until I go an entire night without such issues, but early signs are good - at the very least this has considerably improved the situation.

PSA EDIT: Check your receipts for deposits on loaner tools. I was told was the associate at O'Reilly Auto Parts that I had seven days to return the socket, turns it was 48 hours and I was within an hour of losing my money. Manager was the one who processed the return and looked at the name of the associate on the receipt with GREAT ANNOYANCE when I revealed that little gem(after he remarked that I was cutting it a bit close, I was understandably confused).

 
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Okay, over the past three nights, I have had two nights with rough idles, and one completely free of rough idles.

The two rough idles were very minimal, except for the fact that as I arrived home last night I had one that was almost as bad as when it felt like the car was about to stall. Last night was EXTREMELY cold(single-digit weather), the night I had no rough idles was very warm(near 40). The remaining night as barely below freezing, and I almost couldn't feel those rough idles. I have had no discernible hesitations to accelerate, and only one "rough" start - and it wasn't even something I would worry about as it was a common cold weather start issue(engine was cold and one cylinder didn't completely turn over with the others so the engine vibrated heavily for a second).

I am going to clean the MAF Sensor again just to cover all bases, but if that doesn't change anything should I bother replacing it? (I am off work two of the next three nights so it will be a while before we have a definite answer on if the cleaning worked)

 
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i would

 
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Okay, coldest night I've had at work since these issues began by a wide margin(-1F!!!!!!) and had a LOT more rough idle... But still far less than I had on my previous low-temperature bar before replacing the O2 sensor. First time I've had the level of rough idle where it felt like it was nearly stalling, but even then it was discernibly LESS rough than the last time I'd felt that. While it's not predicted to drop that low again, low teens to high single-digit overnight temperatures are in the forecast for the forseeable future, so my next night at work will likely tell us very quickly if this helps.

 
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consider a IAT (intake air temperature) also.
from google search:
"The Intake Air Temperature Sensor (IAT) is used by the ECU to determine the temperature of the air entering the engine. This is used in conjunction with the MAP sensor to determine the density and volume of air entering the engine to make the proper fuel adjustments to maintain the correct air/fuel ratio."

Honda uses a conjunction of IAT/MAP (Manifold air pressure)
from google search:
"The manifold absolute pressure sensor, or MAP sensor, is used to measure the amount of air flowing through the intake system and into the engine. The sensor sends airflow rate data to the Honda engine control unit, or ECU, which can then adjust the air-to-fuel ratio for optimum fuel combustion."

from google results:
"What happens when an IAT sensor goes bad?
Rough idling and rough running

Engine stalling, rough idling, engine stumbling, and random surges of power are commonly associated with IAT sensor failure. These are concerning symptoms, and they can only worsen with time"

from google results:
"What happens when your map sensor goes bad?
If the MAP sensor goes bad, the ECM can't accurately calculate engine load, which means the air-fuel ratio will become either too rich (more fuel) or too lean (less fuel). ... This leads to excessive fuel consumption, poor fuel economy, and possibly detonation. Lack of Power."

 
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I looked into the MAP sensor thing for a while and could never find any info on one for my car. I couldn't even find a part number for it. When I look up the IAT sensor location, however, I keep getting diagrams of the MAF sensor - that's why I'm plotting to replace the MAF sensor anyway, I was wondering if that might be an issue. If I'd found this out before I replaced the O2 sensor I'd have done the MAF sensor first, but since the car has run so much better with the new O2 sensor I can't really be upset that I did that, since it indicates the old one may have been on the way out anyway.

 
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oh, shoot, for some reason i read 2001 car, not 2010... R18 engine, not D17...

yeah. map sensor, don't see IAT...

 
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It looks like the IAT is integrated into the MAF sensor, which makes sense given location and purpose. I picked up a Duralast replacement at Autozone and I'll install it tonight or tomorrow(don't work tonight, so no real need to rush).

 
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Be better to get one from a junkyard rather than a duralast one

 
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I buy Duralast because I've never had an issue with them, and they have a lifetime warranty in case of the unlikely event that they do go bad.

And only an idiot goes to my local junkyard. It's run by scumbags who will actually look up the part you need and charge you the price of a brand-new one for it. If you're paying new part price, just get a new part.

 
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You need a better junkyard then,
Hondas don't like aftermarket sensors and electronics, so don't be surprised if it doesn't work

 
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No argument there. Unfortuantely there aren't any others in the area. The owners are very old and likely won't be able to run it much longer, so hope it someone with sense buys them up.

Well, the O2 sensor has certainly improved things thus far.

 
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Yep Denso/ntk is the oe brand

 
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Oooookaaayy.... Interesting night on the new MAF sensor. It took longer to settle in than I expected, which worried me, but it eventually did and once it had, things ran mostly the same as they have been on previous nights of similar conditions. There were two differences of note:
1) Near the end of the night a rough idle bad enough that the engine stalled when I hit the gas(rough idling so bad I was afraid it would stall is nothing new, though, just less common after the O2 sensor swap). But had nothing like that afterwards.
2) I AT LONG LAST GOT A FRIGGIN' ERROR CODE. (it tripped three times, same code each time - never tripped while idling, though - always while at speed)

The error code actually excites me a bit since it can point us in a direction to look. Unfortunately, it was a fairly generic code with a lot of potential causes: P0172 System running rich (bank 1).
But still, we now know my issues are being caused by RICH air/fuel mixture, not LEAN, and in looking at potential causes, something did jump out at me in the many places listing potential causes: Thermostat and/or coolant temperature sensor switch.

Even as I write this, it seems a strange thing to be causing an issue with the air/fuel mixture, but the thing is I have a correlation that possibly points to causation. I never mentioned this before because it was so minor and I couldn't even be certain that it even was an issue to begin with, but I have on occasion noticed the engine warm up much faster than usual - it never got hotter than normal(not that I could discern on the temperature indicator, at least), so I considered it a minor thing I was going to bring up at my next standard maintenance in a few weeks. It always happened on the REALLY COLD nights, this is only the second full winter I've owned this car, and last winter was extremely mild with only a couple of bitterly cold nights, meaning I had fewer chances to notice if this was normal behavior. But after seeing the thermostat/coolant temp switch cited as potential causes of a rich mixture, I can't get this correlation out of my head.

So now the question is, given the correlation, should I look into this right away, or is there something else we haven't covered that should be looked at? And which of the two pieces should I look at trying first? (or should I just do them both?)

At this point, the only other thing I'm thinking it could be is a blockage in the exhaust system, but I've had that on cars in the past and it always triggered error codes a lot easier than this did.

 
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Using live data you can compare temperature readings between the coolant and intake temp when the car is cold and warm, see if something doesn't add up

 
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What kind of differences should I be looking for? I don't expect those two numbers to match up even under normal circumstances.

 
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When the engine is completely cold they should be close to each other. You can also verify the readings look correct elsewhere. On a cold start both should be close to ambient, when fully warm IAT will be ~20F above ambient and ECT should be 180-200F.

 
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Okay, so, I took a run down to the grocery store, plus some extra running around to get data. I can say that whether or not it's contributing to the idle issues, there is absolutely 100% a problem with either the thermostat or coolant sensor because the car warmed up WAAAAAAY too fast. I've driven in 99F heat and it warmed up slower. (more on that after the temperature numbers)

When I started the car, coolant was at 72F and intake was reading 55F. Ambient was 23F, but the car was sitting in the garage which was being heated up since my dad was going to do some work on his AMX, and it took logner than usual for the app to connect to the reader, so I think those temperature line up. When I got home, the coolant was reading 174F and the intake was reading 54F when I loaded it up, but dropped to 34F as I was looking at it.

As for the too fast warmup, the grocery store is a 2.7 mile drive from my house. Having only idled long enough to take the baseline reading, my idle time shouldn't have impacted how warm the engine got in that distance by any obvious amount - normal driving, the temperature indicator would have two notches on it after that long a run with normal 35-45 MPH driving.

It had gone up SIX. NOTCHES. Normal operation that car is showing 8-10 notches once up to temperature, and that's where it was when I got home(after an additional 5 miles of test running).

I had rough idles at nearly every stop of varying severity, but no near-stall levels.

So the car is definitely heating up faster than it should be. Which part should I look to first?

To be clear, the car is NOT overheating, just getting up to temperature at a crazy rate, so I don't think there's an issue with the coolant itself. This to me sounds like a thermostat issue, but I'm not sure. I'm tempted to do both parts - neither are terribly expensive and sofar as I can tell both are expected to need replacement around now.

 
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Checked coolant level yet?

 
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Coolant level is fine.

A local mechanic (one we've used for years for stuff beyond our ability and who is very good, trustwothy, and low-cost) that specializes in exhaust and brake work is offering free exhaust inspections for the entire month of February, so I have scheduled an appointment for one. We'll see what comes of that before I drop money on anything else.

Seeing prices for coolant sensor and thermostat I may replace them no matter what since I see that both are parts that are known to often need replacement around 100K miles.

 
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Okay, been a few days, but here's the update. Car appears to be fixed, but I won't be able to extensively verify it tonight as the winter storm has left too much snow for all the roads to be sufficiently cleared and I'll have to borrow my dad's truck.

The exhaust inspection turned out nothing - I am not surprised, it was a longshot, but just from pulling the car into the bay the mechanic agreed SOMETHING was off. So, out of options I can do myself, I booked an appointment at the dealership I bought the car from(an official Honda dealership) since we're now getting into stuff they probably need to do in order to keep my lifetime powertrain warranty valid.

The result: OIL CONTAMINATION. They checked thoroughly for leaks that could have caused it, but found none - Looks like it occurred last oil change. This lines up, as cold temperatures aggravated the issue, and the level of cold that did so was not a regular occurrence until just a few weeks ago, so the problem would not have become apparent immediately.

I was told changing the spark plugs and O2 sensor was a good move, as with the parts nearing the end of their life it probably would've been a lot worse if I hadn't done so(and it helped narrow down the cause). They drained the oil and did everything they could to make sure the contamination is cleaned up, but I have been advised to do my next oil change at the normally scheduled time(which will be in 2-3 weeks) just to be sure.

 
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really?!? Did they find out what was the contaminant to cause such issues?!?

 
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I doubt it since they couldn't find a leak. But the fact that the issue was aggravated by cold weather indicates to me that it was likely something with a high water content - maybe even just water alone. Even I know it doesn't take much to throw off the balance in an engine.

BTW, the mechanic who did the exhaust inspection said afterward he genuinely loves this line of Honda engines. As he put it, "they just don't like to break." :P

 
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anyway, glad you solved the issue.
baffled by the cause... 1st time seeing or hearing that.

 
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First time seeing, not my first time hearing. I'd bet money some water accidentally got in while they were filling up last oil change. While it wasn't terribly cold, it was very WET at the time - as in the "water splashing onto every component even if you're only going 5 MPH" type of wet. May have only taken the minutest lapse in attention for JUUUUST enough to drip in there somehow while the oil filler cap was off.