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Dave · 03-19-2018 06:21 PM

Because i did some tests on how the iacv works and the help of popgun we know that the iacv is a busy part, it does a lot of work around the normal idle position, because the way the software inside the ecm is written every time the throttle moves the iacv is told by the ecm to move a few steps in the same place, in anticipation of the real reason why this is the case my thinking is that some of them do not stand up to this amount of work in this spot and have difficulty moving small amounts, they are quite delicate parts operating in a hot place, but when the engine is restarted the iacv does some more traveling and is able to overcome the sticking point and temporarily behave as normal, again, just my unconfirmed speculation.
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This is a great explanation Max, thank you! This cleared up a lot of questions I have been asking myself.

Dave · 03-21-2018 07:16 AM

Update. I performed a test suggested by Max, and here are the results: I unplugged the connection to the IACV and rode the bike yesterday. The temperature was 58 degrees, and the bike had not been started in 24 hours. The engine started normally, and idled at about 700 RPM initially. I’m not sure if it would have stalled if I allowed it to idle by itself, but I warmed it up for about two minutes by gently blipping the throttle before going for a test ride. I rode about three miles of stop and go on city streets and as the engine temperature rose, so did the idle RPM. It reached a steady, smooth idle of about 950 RPM before I turned it off, and there was no indication that it would stall. I let the bike sit for about one hour before restarting, and then took it for a longer ride that included stop and go, and about three miles on the freeway. The engine was fully warmed up on this ride, and it settled into a nice, smooth 1,000 RPM idle. There was no indication of stalling, and it never dipped below 1,000 RPM when allowed to idle. I do believe I felt a slight loss in power (very slight), but other than that, the bike ran perfectly. The idle was smooth and repeatable at every stop, it never dipped below 1,000 RPM, and the engine never missed a beat. This test was performed under cool conditions, so I don’t know if it would be repeatable under more severe (hotter, more stop and go) conditions.

On another note, my bike has never experienced the increased RPM when in 1st gear, as the clutch is being let out, as described by other members. Probably 90% of the time I wait until I feel the clutch begin to engage before applying any throttle, so I believe I would have noticed this condition if it was present. This new idle condition described by some members is interesting, and I we can find out if our bikes are designed to do this.

pdedse · 03-21-2018 07:25 AM

(03-21-2018 07:16 AM)Dave Wrote: ... I unplugged the connection to the IACV and rode the bike yesterday. ...and then took it for a longer ride ...it settled into a nice, smooth 1,000 RPM idle. There was no indication of stalling, and it never dipped below 1,000 RPM when allowed to idle. ...

With this information does Dave now have "probable cause" that the IACV is the culprit?

**The ferret** · 03-21-2018 07:41 AM

(03-21-2018 07:16 AM)Dave Wrote: On another note, my bike has never experienced the increased RPM when in 1st gear, as the clutch is being let out, as described by other members. Probably 90% of the time I wait until I feel the clutch begin to engage before applying any throttle, so I believe I would have noticed this condition if it was present. This new idle condition described by some members is interesting, and I we can find out if our bikes are designed to do this.

I don't know if you would have noticed it Dave, because who puts their bike in gear during cold start high idle and lets out the clutch without their right hand being on the throttle? That is not a natural thing to do. It never would have occurred to me to even try this had it not been discussed in this thread. I might do it one more time as an experiment once the weather warms up, just to see if it's a cold weather thing, but I rode my bike 91 miles the other day and it was perfectly normal as far as I am concerned..but.. I let the bike do it's normal cold start idle thing, when it dropped down to 1050 I dropped it in gear and let out the clutch feeding in throttle to move out.

SportsterDoc · 03-21-2018 08:38 AM

(03-21-2018 07:25 AM)pdedse Wrote: With this information does Dave now have "probable cause" that the IACV is the culprit?

Dave ordered a new IACV from his Honda dealer.
The part is backordered, so there may be a delay in receiving the part.
Dave emailed that he is loyal to his dealer and choose to not order on-line and his dealer gave him a price as good as/close to on-line.

A couple weeks ago (post 726) I commented: "Even though the IACV operation is a prime suspect in most of the reported idle issues, there may be (instead of or in addition to) poor electrical connection(s)."

This may have been Max's direction earlier than that, but Max wanted to be sure that all other possibilities were checked, since replacing the IACV will take more labor than the other checks.

The only other step which may be practical to do, waiting for the new part, would be to unbolt the IACV (air box in place), pull it back enough to squirt some silicone lubricant into the area, which may facilitate easier movement (or not?)...the theory being that if it is binding, the IACV may not in itself be defective, but not able to operate properly.

Previously posted:

It does not seem to be a MAP issue, due to symptoms not matching.

It does not seem to be an EOT issue, per reports in this thread and symptoms not matching

It does not seem to be a TPS issue, due to the recent testing guided by Max. There may have been one or two TPS issues, but not for Dave.

Manual pages 5-74 and 5-75 cover IACV (symptoms seem to match): One check is to listen for the sound of it cycling with key on and stop/run on. There is a caution about cleaning before removal to prevent debris in the IACV passage...therefore, any debris would be a concern to proper operation.

Note the symptoms/fail safe function of all DTC on pages 5-15 and 5-16 of FSM.

In the b&w photo at the bottom of page 5-74, it is not sufficient quality to see any air ports to the sides of the passage. If IACV replaced, without cleaning, an IACV issue may remain.

The IACV is 16430-MJF-D01

The IACV can be tested, per the factory service manual:

IACV testing, per FSM 15-41 & 15-42:

Note: These tests may be done with IACV mounted, by lifting rear of fuel tank and removing right side throttle body cover.

1. After clearing stored DTC, per page 5-14, recheck for stored DTC 29-1. If none, then prior DTC was intermittent.

2. Measure resistance of each of the four wires at the ICAV connector (disconnected, harness side, not IACV side). Continuity to ground should be infinity. If not, the wiring harness has a short to ground.

3. Check continuity to ECM, from disconnected ECM 33 pin to disconnected IACV 4 pin connector
Positions are numbered with locking tab up:

ECM A6 black/yellow to IACV connector postion 1 (left)
A17 black/red, position 2
A16 black/blue, position 3
A7 black/orange, position 4 (right)

4. Measure IACV resistance, (IACV side, disconnected), facing with locking tab up at airbox side (mirror image of connector):
position 4 black/yellow (right)
position 3, black/red
postion 2, black/blue
position 1, black orange (left)
a. black/yellow to black orange (2 outside positions), 99-121 ohms at 77F/25C
b. black/red to black/blue (2 inside positions), 99-121 ohms at 77F/25C
If resistance out of spec, FSM declares IACV faulty

My 2 cents: If IACV and wiring tests good, then if symptoms continue to point to IACV, it may be a piston travel issue or air port issue.

Until Dave advises further, I am trying to make this post a summary, to date:

Max started a very comprehensive thread on the IACV.

http://cb1100forum.com/forum/showthread.php?tid=12203

Post 9, Feb 19:

vacuum loss (minor = high idle, major = close to stalling/stalling)
TPS (FSM symptom/fail safe: hard to start cold)
IACV (FSM symptom/fail safe: engine stalls, hard to start, rough idle
EOT (FSM symptom/fail safe: poor acceleration)

DTC 29-1, FSM page 5-16, lists IACV circuit malfunction as "loose or poor contact of IACV connector, IACV or its circuit malfunction".

Otherwise, per the FSM, other sensors failsafe is normal engine operation, this includes MAP, IAT and O2. There is no mass flow sensor or exhaust temp sensor on the CB1100.

The FSM incudes all sensors on pages 5-15 and 5-16.

Symptoms reported are classic for IACV.

The piston not moving as much as the stepper steps would not likely provide a DTC (opinion) and this may be more likely than any other aspect of the IACV operation.

Post 11:

Just glancing at pages 5-15 and 5-16 shows how well the CB1100 will continue to perform with many sensor codes.

If the EOT is wonky, the only issue is hard starting cold.

If the IAT is wonky, default is 95 F.

If TPS is wonky, default is 0 degrees position

If an O2 sensor is wonky, "engine operates normally"

However, if a fuel injector faults, it is time to push: Engine does not start, injector power, pump and ignition shut down in the event of "loose or poor contact of the fuel injector connector-fuel injector or its circuit malfunction"...fail-safe is not just complete failure...it is out of spec parameters.

Post 16:

The "advantage" of purchasing the entire throttle body assembly (solved 203 issues) is that the IACV port would be clean, not warped, with new IACV and new TPS.

...hearing the IACV cycling indicates that the stepper motor is stepping or trying to step. If crud is preventing full operation, it may not sound much different. The ECM has no feed-back regarding actual movement.

max · 03-21-2018 02:15 PM

Nice one Dave, steady idle during the last test and not even in limp mode either?

Thinking what could go wrong in assembly; the throttle body would be assembled in one piece away from the bike and later mounted to the engine before insertion into the frame.

Have they screwed the piston in completely before inserting the iacv into it's cavity,
Is the shaft straight before mounting, was a box dropped before assembly?
Was the iacv screwed in on one side first and damaged the piston/shaft?
Has someone not lubricated some parts or used the wrong lube?

Guess you will be the first one to know what made the detective story happen in the first place.

So one thing that would be interesting for the future is if you have the old iacv unplugged just like now see if you can plug the new one in and fool the ecm so that it thinks the iacv is still connected ( no check engine light ) and see if that makes a difference in the way it drives as you mentioned there seems less power, this can still be done once the new one is in place, and as a bonus you get to see how the iacv operates on startup and during a ride.

We would all like to see pictures side by side of the iacv's as it came out of the tb and it would be a good idea to measure the distance the piston is extended from the iacv body so we have a record in which part of the travel we can expect erratic behaviour.

And if you can make a video of the same side by side showing them 360 degrees closeup and sharp maybe we can get a better idea what the problem was, Magnus's pictures were good but better resolution and more of them would be very nice for the future and possibly convince Honda dealers why this happens.

What i expect you find is a slight binding in travel of the piston in the area when it is removed, and are any of the piston parts plastic?

Congratulations Dave!

SportsterDoc · 03-21-2018 02:36 PM

(03-21-2018 02:15 PM)max Wrote: Nice one Dave, steady idle during the last test and not even in limp mode either?

Other than the apparent ECM program, on some bikes, which increases idle as clutch is released, it would seem that unplugging the IACV would eliminate a fast idle.

Any further comments, Max?

Dave · 03-21-2018 05:26 PM

I don't know if you would have noticed it Dave, because who puts their bike in gear during cold start high idle and lets out the clutch without their right hand being on the throttle? That is not a natural thing to do. It never would have occurred to me to even try this had it not been discussed in this thread. I might do it one more time as an experiment once the weather warms up, just to see if it's a cold weather thing, but I rode my bike 91 miles the other day and it was perfectly normal as far as I am concerned..but.. I let the bike do it's normal cold start idle thing, when it dropped down to 1050 I dropped it in gear and let out the clutch feeding in throttle to move out.
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Actually, I am convinced I would have noticed this. I have never waited long enough for my cold/high RPM idle to drop before riding off (how long does this actually take?), and I usually do not just drop it into 1st gear at a dead stop when it is idling high either. I wait about a minute to give the engine some time warm up, then I push the bike forward as it is idling so that it begins to coast down the slight hill in my driveway. After I pick up momentum I pull in the clutch and drop it into 1st gear, and I do not apply any throttle before I feel the clutch begin to engage (there's no need to apply throttle when the engine is idling high anyway). My engine RPM has never increased when I have done this. I am wondering if this is normal for our bikes, or does this just indicate that something else is wrong with my bike?

Congratulations Dave!
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Please, it's too soon for congratulations! I have thought that I cured the idle problem three times now, and each time it was not to be. The first time was when I replaced the EOT sensor. The second time was when I tightened the clamps on the throttle body. And the third time was when I drained and refilled the gas tank with a different brand of gas.

I would have more trust in the results of this latest test if I could repeat it in much warmer conditions (80 - 90 degrees, versus 58 degrees), and if I put a lot more miles on it during the test, particularly stop and go miles.

I will take pictures of the old and new ACV, and post all of my comments.

**The ferret** · 04-06-2018 06:01 PM

(03-12-2018 03:32 PM)The ferret Wrote: Ok I went out and tested my 2014 DLX. Fired it up and it went to 1400 ish rpms normal cold idle. Dropped it into first and without touching the throttle let out clutch to just before engagement point and the idle went up to maybe 1700 rpms. Did this several times to verify. Let the clutch out any further and it starts pulling forward. Very Interesting.

Then I put it back in neutral and let it continue warming up until it got down to the 1050 ish rpms normal warm idle. Dropped it into first and without touching the throttle, let out the clutch to just before engagement and the rpms DROP to near 800 rpms. That's as low as I could get it to go before engagement started and bike started pulling forward.

So on cold idle a rise of near 300 rpms and on warm idle a drop of near 300 rpms by putting in gear and letting clutch handle out to near engagement point.

Interesting, today I tried repeating this. I pulled it out of the garage, fired it up, it immediately went to normal cold idle, about 1400 rpms. I dropped it into first, and without my hand on the throttle let out the clutch until it started to engage. Today the idle went DOWN as usual, not up like before. I did it 3 or 4 times. Each time the idle dropped as I got near engagement.

The only difference I can think of, is last time it was probably near 32 degrees, when I tried it, and today it was about 50 degrees. Can't explain it.

SportsterDoc · 04-06-2018 07:32 PM

(04-06-2018 06:01 PM)The ferret Wrote: Interesting, today I tried repeating this. I pulled it out of the garage, fired it up, it immediately went to normal cold idle, about 1400 rpms. I dropped it into first, and without my hand on the throttle let out the clutch until it started to engage. Today the idle went DOWN as usual, not up like before. I did it 3 or 4 times. Each time the idle dropped as I got near engagement.

The only difference I can think of, is last time it was probably near 32 degrees, when I tried it, and today it was about 50 degrees. Can't explain it.

Only a guess: Based on IAT and/or EOT input(s), the ECM affects operation of the IACV. Be interesting to see ECM program code.