2000 Honda Civic EX D16Y8 Engine, Recurring P0505 IACV set at low idle

Hello Scanner Danner Repair Forum:

I've got a 2000 Honda Civic Ex with a stock D16Y8 engine; many repairs have solved
many problems; the last one is a recurring P0505 IACV that sets at low idle.

Here's the history.

Owned since 2012, was 143,000 miles when bought; (just turned 200,000).   Had a slow oil leak
which got worse over the years and started gushing in May 2021. It always had an idle that when
you took your foot off the accelerator at a red light the car   would move forward so you had to
stay on the brake.  Tried to get it repaired, no success,  just lived with it. (Probably why the cat burned out)

Feb 2020: P0420 Catalytic Converter code check engine light came on, Covid shutdown started
March 12th 2020 for me and car was very infrequently driven.

Spring 2021: started YouTube University to learn how to fix the car and pass inspection.  Eric the Car Guy, 
and others have been my gurus and Eric's video with Scanner Danner led me here and now I'm going to
buy the book and become a Premium member and really understand what's going on!

Started on oil leak problem: PCV valve blocked, hose collapsed, breather box oil ring leaking.
   - removed IM to get breather box off; replaced O ring, grommet, PCV valve and tube
   - cleaned IM and intake ports on engine head
   - replaced IM gasket
   - cleaned TB, replaced TB gasket
   - cleaned IACV and drained coolant
   - put in distilled water and Prestone flush cleaner, burped system
   - replaced VTEC solenoid gaskets, oil leak better
   - replaced oil pan gasket, oil leak stopped
   - replaced complete exhaust system from down pipe back with Walker parts including cat and Denso O2 sensors; P0420 and O2 codes gone
   - Had a hunting idle ; had cleaned IACV before, replaced with a NAPA IACV, still had hunting idle, made a smoker found vacuum leak; cruise control
     hose was off, hunting idle went away.

Now there's no oil leaks, the exhaust system is good,  it starts up fine, it drives nicely until it is warmed up
and when stopped idling at 1000rpm at a red light for a long time I will see the idle suddenly drop to ~900 rpm and
then start stumbling, hesitating, losing power, with a flashing check engine light, hesitating, jerking as you try to get it to move.
When the codes are pulled it shows a pending P0505 and a stored P0505 of severity 2 of 3.

I've been driving back and forth to work only (about three miles); it only begins to hit operating temp by the time I park it at work
and when stopped at a red light I put it in Park which raises the idle a bit.  Can't go on like that!

I have an Innova 5410 scan tool and get some data that's stored when the code sets but I'm unable to get live data even though
the tool is supposed to be capable of live data.  I spoke to Innova's tech support and they tell me it's a limitation of my 2000 Honda
not sending the data.  My inspection station guys tell me that if that's the case that an oscilloscope is the only way to diagnose it.

ScannerDanner support (Kristin) told me that oscilloscopes are covered in the book and class, so I'm checking out the ebook first but
will probably get the hard copy book to take notes from the Premium classes.  I'm going to buy the ebook tomorrow to get started,
but here's my summary of my problem to start, Tyler and Andy.

It would be awesome if there is a quick fix to my idle problem so I can get off pins and needles and drive the car somewhere else
than just work   But I'm starting at Chapter 1 and learning it all til I master all the material and am prepared for any problem!

Thanks!
CaseyAtTheBat







 

I'm pretty sure that when the CEL starts blinking it's because the PCM is detecting a pretty serious misfire in progress and that the engine needs to be shut down before cat damage occurs. That may have been what sunk your last cat and could happen to your new one (and very quickly) if you aren't careful. The stumbling/loss of power you mentioned you're having certainly could be a result of a misfire. Is your scanner capable of accessing mode 6 data? If so, you ought to be able to check the misfire counter under it to see which cylinder is suspect. I don't buy Innova's story that your Honda just doesn't support live data, but I am no expert. In their defense, however. unless you're using a factory supplied scan tool, not all of a scanners' functions will work as advertised on all vehicles, no matter how much you spend. You may want to try to try using a different brand of scanner and see if you can access it. Autozone may rent one out, if you have one near you

Sounds like it might be a high idle setting the P0505.With no scan data could maybe try unplugging the IACV, with the engine up to temperature, to see if RPM changes as a starting point.

Agree with ksat22 that the vehicle also has a misfire problem which should be investigated first.

I have a thinkdiag, you can get them on Amazon for like $60 for a single car. It has worked well for me on several cars. And pretty sure you have a bad misfire.

Sent from my SM-N970U using Tapatalk

If the mechanical throttle butterfly stop screw has been twiddled with to increase the idle it can really confuse the IACV control on most engines

Thanks for all the replies!

ksat22:  I spoke to Innova to ask them about mode 6, the tech support line guy didn't know what it was so guess it doesn't have it.  I was told by my inspection station/repair shop that if you can't get live data it needs to be diagnosed with an oscilloscope so I'm ready to buy one of those and learn how to use it with the book and Premium. 

Wow, misfire.  I tried to be concise with the history I wrote, what seemed most relevant to the current problem.
Other history is:
May 2021  P0302 misfire; replaced spark plugs with new NGK, misfire stopped
June 2021 P0335, P0336 Crankshaft Position Sensor, replaced Distributor; lifetime warranty swap of a Carquest distributor, stalls and codes gone
July 2021 Did all the oil leak work mentioned in previous history, oil leak gone, still exhaust codes
August 2021 another misfire P0301, #1 spark plug carbon fouled, replaced with new NGK , misfire gone, still exhaust codes
Sept 2021 Replaced Exhaust system, cat and O2 sensors, also replaced oil pan and gasket, Oil leak totally gone, exhaust codes gone
                 had a hunting idle, replaced IACV with NAPA IACV, still there, found vacuum leak, hunting idle gone.
Oct 2021 Started driving car to work; heavy downpour once, had to drive through some water, misfire started again. 
                Found moisture in distributor and some corrosion inside one terminal; dried and sanded to bright metal. Found damage to #1 spark plug wire  
                like an animal chewed on it.  Replaced with OEM spark plug wires. Checked spark with a Lisle spark plug tester, cleared codes, misfire gone
                engine ran smoothly.

But...
The idle, which had always been too high continued to settle to 1000 rpm.  And as I described earlier, it runs great, very peppy, it is only when it has been sitting at idle, usually at a traffic signal, that I'll see it suddenly drop to about 900 rpm, (like the computer is doing it?) and then start this roughness, a loss of power when I try to accelerate away from the traffic signal, a jerking as I try to finesse the accelerator; when I get it into a higher rpm it gets smoother but still not normal.  I got to work and parked.  When I start the car up at the end of work, it starts up like normal, and I got home,
the stored code is P0505 IACV, no misfire codes.
Since then, if I put it into Park at a traffic signal and the idle goes a little higher, then I put it into Drive when the signal changes, it continues to have normal power and smoothness and I get home fine. I went on a farther trip once and it seemed like it was on the verge of starting this on the way home and that's when I tried putting it in Park for the first time and it got home fine and did not store a code.  Since then I only go 3 miles back and forth to work, and put it in Park at signals, no roughness, no codes.

Okay;
Matt T, I'm going to try your suggestion of unplugging the IACV at optemp, I'll post the results!
Andy.MacFadyen:  I've never touched it and all the articles I've read and videos I've watched say "Don't touch it!" but it has occurred to me recently
                            that maybe it was moved in the past.  I'm such a nooby that I'm leery to touch it until I know more and have a scantool/oscilloscope
                            to get data about what's going on.

So I'm ordering the e-book now to get started.

What do you guys think about all this?  Oscilloscope the way to go?   Is there an entry level/not too expensive one that you can recommend that will do
the job for a beginner DIYer like me?
               
 

Idle hunting on a map engine is usually the result of a vacuum leak. The iac is a result not the cause. You found this true prior. Smoke it again. It's probably a small gasket leak.
Base idle is 750 with engine hot and iac disconnected. If it's stalling it's base idle. If it's hunting it's a vacuum leak.

Okay, Matt T here's the results:

Arrived home from my 3 mile drive home, up to operating temperature.  In my driveway with the engine running and idle on my dashboard tachometer at 1000 rpm I unplugged the IACV.  The idle went much higher!  I looked at the tachometer and the idle was about 1700 rpm with a little flutter that you could see in the needle on the tachometer dial and hear in the engine sound.  It was NOT hunting up and down.

I shut the ignition off and there was a check engine code light on and I read it with my Innova 5410 scantool; P1509 (1/1) Stored IACV Circuit Failure, which seems understandable since it was unplugged.  When a code is stored, some data is stored too with this tool although no live data is available.
Fuel System 1 CL
Fuel System 2 N/A
Calc Load  34.9%
ECT    190 degrees F
STFT B1 10.2 %
LTFT B1 6.3%
MAP   10 in Hg
Eng RPM    1342
Vehicle Speed   0 mph
IAT 88 degrees F
TPS    9.4%

Well, what do you think of that result?   What does that indicate?  I was so surprised, I thought it would drop!

Scannerjohn, thanks for your post!  It/'s not a hunting idle now; it remains steady at 1000 rpm.  When I had smoked it previously when it had a hunting idle and found the cruise control hose off, I had looked carefully all over especially because I had replaced the IM gasket and the TB gasket.  I didn't see any leaks there or anywhere in the air supply tube. 

I bought the e-book today and got started. 


 

Interesting. I guess the IACV is normally open. And the PCM is controlling it. I'm thinking the high idle is either a vacuum leak or base idle setting.

Looks like that's the freeze frame data, which is a snapshot of things at the time the code set.

Anyway, your fuel trims are too high there. LTFT should ideally be around zero and STFT should ideally be between -0.5 to +0.5. Combined they shouldn't be more than +/-10, I believe, yet you have +10 on the short term alone. The PCM is trying to push things rich due to some problem, which you have to figure out (a vacuum leak can certainly be one reason).

If the injectors are actually putting in as much fuel in as the PCM is telling them to, I just want to reiterate that your new catalytic converter probably won't be lasting long.

Okay...  wow, looks like a smoker test is next!   Scannerjohn, looks like you were on the right track
even without having the unplugged IACV data.

ksat22, thank you for conveying the cat concerns and the urgency!  Must go back to work now,
tomorrow mid-day I'll be able to do the test. I'll post the results.

Thanks so much for the interest and support and the incredibly swift replies.
CaseyAtTheBat

 

Broke out my DIY smoker and took off the air tube from the air box to test there first,
then the TB etc.

Don't know if it had a crack to begin with but now it's torn half way through
where the ridges are!

Never a dull moment...   I've wrapped it in electrical tape, was able to start up
the engine, sounds the same and fingers crossed it will run the same on my
sprint to and from work.

Honda discontinued the part; I've got a used one coming from Beaver's Car Salvage
in Charlotte NC who specialize in used Honda and Acura parts. Will get here next week!

Next I'll test at the TB to see if there are any visible leaks anywhere.

Car drove the same with the electrical tape wrapped around the torn air tube.

Tested for vacuum leaks today.  Used my DIY smoker attached to the TB circular
opening before the throttle plate; no leaks to be seen from the TB or IM or any
where else in the engine area.

I've got a bicycle plump hooked up to the smoker to pressurize it.  I pumped it
slowly for a long time and used a flashlight to look everywhere very carefully.
So I guess it's not a vacuum leak.

Any thoughts on where to look next? 

I started the ScannerDanner Premium and the book and started on the Electrical Basics
as Paul suggested for noobys.

Thanks.
CaseyAtTheBat

Coolant update.

Had previously found the overflow bottle down to the minimum level about
a week after the system had been drained, filled with distilled water and
Prestone flush cleaner to do a first flush and repeatedly burped with a
spill-free funnel.  I'd topped it to the maximum line.

Hadn't looked at it since.  Checked it on Sunday; overflow bottle empty.
Opened radiator and started putting in distilled water till full; took about
a half a quart!  Then filled the overflow bottle to the maximum line.

Drove to work the same this morning, park at lights, no problem.

A first frost to freezing temperature is forecast for tomorrow night;
must get antifreeze in the system.

Drove to Napa for more Prestone to do another quick second flush and grocery
store for more distilled water. Drove around my neighborhood for long time
stopping and starting without doing the put it into Park thing. 

No codes, ran very smoothly.  Oh my gosh, is it possible that the problem was air
in the coolant system?!

And now I've got to drain it again!

The idle is still too high, so there's much to straighten out and I've got to figure
out how to get live data from this thing.   Again, anybody have recommendations on a DIYer
oscilloscope?
Thanks,
CaseyAtTheBat

So what happens when you hit the LD button on the 5410 scanner? No info comes up? I have the Innova 5610 and have not been very impressed with it. I recently upgraded to a Thinktool Pros but that is a huge increase in price compared to what you have.

I have a 1 channel Uscope from AES Wave that is pretty nice for the DIY'er and if you don't get the master kit, is pretty reasonable on price. That might be a good place to start for a scope.

Update

I drained the coolant the day it was supposed to freeze at night and then filled it with 50/50 Honda Coolant,
and burped it for over an hour while the radiator fan came on and off numerous times.

(By the way, since you only get about half the distilled water out, how can you really end up with a 50/50
coolant/water mixture and get the necessary low temp protection? I'm in the suburbs of Philadelphia, PA
so the worst it ever gets is about a short snap to 10 degrees.)

Drove it that way for the rest of the week, sprint to work and back and did less and less of the put it in Park
thing and ran smoothly!!

I think the problem was all due to the coolant system having air bubbles that hadn't been fully burped out.

Well, that weekend I did two more flushes (til I got to clear distilled water) and then filled it with the 50/50
again and burped it FOREVER.

Drove it to work and the hardware store, felt like I was flying... Problem solved!!! (Still have to investigate
base idle though).

Next day, driving in for the afternoon run (school bus driver) THE TRANSMISSION BROKE DOWN

Dealing with that, getting a remanufactured trans from Reman Transmissions, 5 year warranty,
putting in new rear main seal while it's out. (200,000 miles)

Getting there....

Thanks 70monte for the post!

Yes the 5410 just twiddles its thumbs for a long time when you push the button for Live Data and eventually gives a message that I can't remember now that says it's not available on this vehicle. I spoke to their tech support and the answer was, it's just not available on this vehicle even though it is OBDII, probably due to it's age (2000) they said.

Thanks so much for the recommendation, I'll check it out. I guess it's the same website where Paul sells his book from too.

As you can see from my previous post I'm all wrapped up in getting the transmission fixed but I'm on Basic Electrical Concepts in Premium
.
Thanks!

"(By the way, since you only get about half the distilled water out, how can you really end up with a 50/50 coolant/water mixture and get the necessary low temp protection?"

Refill with full-strength antifreeze and use a tester to make sure you're at the proper freeze protection.