CB1100 Idle speed instability problem

[17-CB-002]

I've seen a few idle speed instability complaint on the CB1100', there's too many pages to read, so I only read a few treads.
Let me explain the proper operation of the Idle Air Control Valve (IACV).
Construction of IACV:
The IACV valve consists of 4 coils and a rotating plate.
The plate covers/uncovers an air bypass passage to control the required speed.
Each coil resistance is roughly between 90 ~ 120 ohms.
ECM idle speed control:
From the ECM internal schematic on the IACV diagram, the ECM controls the idle speed via the 4 coils inside the IACV.
The ECM grounds the coils in sequence to control the air bypass opening.(1A pin A6, 1B pin A7, 2A pin A17, 2B pin A16)
Example:
To increase the air bypass therefore more speed; the ECM grounds in sequence 1A, 1B, 2A, 2B (repeat if necessary) so that the plate rotates CW and uncovers the bypass port.
To decrease the air bypass therefore lower speed; the ECM grounds in reverse sequence 2B, 2A, 1B, 1A (repeat if necessary) so that the plate rotates CCW and covers the bypass port.
As an example, (I am assuming) from "fully" closed position to "maximum" open position there are 80 steps
If you have a HONDA scanner you can monitor the number of steps at idle.
Now let's say the engineer decided that with a fully warm up engine when the ambient temperature is at 71 F, the steps (count) should be around 30 steps for 1000 RPM (Now this 30 steps is now known as the idle "target" speed and the ECM will try to bring the IACV opening to 30 steps so that the engine speed is 1000 RPM.

But in real life situation if there is an air leak after the throttle body and in order for the ECM to maintain that same 1000 RPM, the ECM now has to decrease the IACV steps (closing the bypass port) to let's say 20 steps to compensate for air leak.

Now, if the is an intake restriction, the ECM will increase the IACV steps to let's say 40 steps to let more bypass air in (opening the port).
If you have a scanner, you can immediately deduct that the IACV is closing or opening the bypass port to compensate. So having no scanner one is a just guessing game.

What important input sensors are required for the ECM to decide the idle speed.
1. The Throttle position Sensor will tell the ECM to control speed for idle. (most important signal for idle speed)
2. The MAP sensor will tell the ECM how much air is entering the engine.
3. The Engine Oil Temperature (EOT) will tell the ECM to compensate for a cold morning start so that you can get a fast idle.
4. The Intake Air Temperature (IAT) will tell the ECM to compensate for air density.

IACV does not easily fail
If coil resistance are on specification, then the IACV may be sticking due to dirt or rust etc. It can easily be cleaned with brake cleaner or equivalent.
Note: Each time when the engine is shut down, the ECM will open the IACV valve to maximum and ready for the next start and then go into sleep mode - and also
because the ECM needs to know its position (which step it is in usually at 80 steps).
Hope this will help understand the operation of the IACV.

[syncronizator_imp]

Hi Alain,

Me and Speed had a problem with engine idling.
We both verified the IACV coil resistance... was OK (according to SM)
As you can see in my movies, my IACV is electrically functional.
Both IACVs were clean. The chambers were also clean
Speed cut his old IACV and didnt notice signs of mechanical damage.
Both me and speed have exchanged IACV.
The problem was solved in this way for both of us.

Do you have an idea how to explain it?

The questions?
What is this device (HONDA scanner) you are talking about and what it is used for ?
Any picture or model ?
How is it used?
Should Honda service be able to diagnose this fault with this scanner?

[Lord Popgun]

the Honda scanner (can't remember its actual name) is (supposedly) available only to Honda dealers. However there are aftermarket alternatives. Healtech makes one. I have one. It cost ~200 and plugs into the diagnostic connector under the left side panel. It also plugs into a Windows PC (not compatible with Apple) and uses Healtech's software that can be downloaded from their site. It communicates with the ECU and will display many engine parameters. You can reset fault codes too.

It makes run files so you can do whatever you are doing, and replay the file at any time. Here is a link to their ODB tool. Of course, I have the one for Hondas.

I last used it to gather information on IACV steps during warmup during our initial testing/investigation when idle problems first showed up.

[peterbaron]

https://www.healtech-electronics.com/products/obd/

[Lord Popgun]

Thanks PB. I forgot to paste in the link

[zirconxi_imp]

My bikes are having symptom these few days during the evening ride back from work, after she start having the issue few days back after I refuel the bike. But its always return to normal during the morning ride to work. And the RPM will only drop to about 800-1000. Did you guy's problem progressively become worst? Such as the RPM slowly drop as time progress?? I haven't have a stalled engine yet. But are starting to get worried as these few evening she started acting up. Is it possible to spray some carburetor cleaner into the airbox thru airfilter compartment and clean up the IACV? It seems there is another chamber between Airfilter and the throttle body, will the carb cleaner be able to reach the throttle body and IACV if I spray into the filter compartment?

[syncronizator_imp]

the Honda scanner (can't remember its actual name) is (supposedly) available only to Honda dealers. However there are aftermarket alternatives. Healtech makes one. I have one. It cost ~200 and plugs into the diagnostic connector under the left side panel. It also plugs into a Windows PC (not compatible with Apple) and uses Healtech's software that can be downloaded from their site. It communicates with the ECU and will display many engine parameters. You can reset fault codes too.

It makes run files so you can do whatever you are doing, and replay the file at any time. Here is a link to their ODB tool. Of course, I have the one for Hondas.

I last used it to gather information on IACV steps during warmup during our initial testing/investigation when idle problems first showed up.

Ok so the "Honda scanner" is just "OBD tool" available everywhere.
THX

My bikes are having symptom these few days during the evening ride back from work, after she start having the issue few days back after I refuel the bike. But its always return to normal during the morning ride to work. And the RPM will only drop to about 800-1000. Did you guy's problem progressively become worst? Such as the RPM slowly drop as time progress?? I haven't have a stalled engine yet. But are starting to get worried as these few evening she started acting up. Is it possible to spray some carburetor cleaner into the airbox thru airfilter compartment and clean up the IACV? It seems there is another chamber between Airfilter and the throttle body, will the carb cleaner be able to reach the throttle body and IACV if I spray into the filter compartment?

Hi zirconxi.
In my case I was coming back from work .... and I noticed that my bike drops RPM to 500.
It happened almost everyday until i replaced IACV 2 weeks ago.
Sometimes the engine went out....sometimes no.
Now I am about 1200km after replacement and it is OK.

My bikes are having symptom these few days during the evening ride back from work, after she start having the issue few days back after I refuel the bike. But its always return to normal during the morning ride to work. And the RPM will only drop to about 800-1000. Did you guy's problem progressively become worst? Such as the RPM slowly drop as time progress?? I haven't have a stalled engine yet. But are starting to get worried as these few evening she started acting up. Is it possible to spray some carburetor cleaner into the airbox thru airfilter compartment and clean up the IACV? It seems there is another chamber between Airfilter and the throttle body, will the carb cleaner be able to reach the throttle body and IACV if I spray into the filter compartment?

It was my idea too.
I didn't try... but ... if the engine can suck air into the IACV chamber, it can also suck in cleaning fluid.
If you try ... let us know if you succeeded.

[Lord Popgun]

Sync,

Our bikes do not have an ODBII port. The HDS is Honda proprietary. But Healtech does make one that works on on Honda bikes/outboards. There may be others. Goggle may be your friend.

[Speed_imp]

My bikes are having symptom these few days during the evening ride back from work, after she start having the issue few days back after I refuel the bike. But its always return to normal during the morning ride to work. And the RPM will only drop to about 800-1000. Did you guy's problem progressively become worst? Such as the RPM slowly drop as time progress?? I haven't have a stalled engine yet. But are starting to get worried as these few evening she started acting up. Is it possible to spray some carburetor cleaner into the airbox thru airfilter compartment and clean up the IACV? It seems there is another chamber between Airfilter and the throttle body, will the carb cleaner be able to reach the throttle body and IACV if I spray into the filter compartment?

In my case it has been progressive, sometimes it cured itself while driving. Then it stalled sometimes when stopping and after that it was stalling even when shifting down before entering a turn. Lately it was behaving always like that.

[zirconxi_imp]

Might be a false alarm on my case. When I open up my air filter, there is maybe a 2mm thick dust collected. I change out the filter and the idle return to normal. Checking back on my service record, it seems I didn't change air filter for almost 24k km. And my work place is in dusty industrial area, 8 hours parking and you can start drawing on the seat. Anyway, will keep monitoring if the idle issue really is false alarm.