CB1100 Idle speed instability problem

[ericlo69_imp]

There are hundreds CB1100 owners in Taiwan, and we have one group in Facebook (HONDA CB1100 riders’ club), we can share information and issue discussion in this group. As of today seveal CB1100 got idle speed unstable problem (Idle speed drop, then engine died; all are 14’ or 15’ model), some are solved by throttle valve assembly or idle motor replacement, some are still suffering this problem. most of them can solve the problem temperally by ignition off/on.

Here I would like to descript one case, one owner suffers serious idle speed problem for one month, his CB1100 is EX version (Y2015, mileage ~ 3000 miles), and symptoms are as follows,
1. Symptom: During riding (engine was in normal operation temperature), suddenly idle speed went up to 1500rpm (normally should be ~ 1000rpm); ignition off/on could solve this problem temporally.
2. Dealer’s actions: throttle valve cleaning, ECU reset…
3. Symptom: After dealer’s action and hours riding, suddenly the idle speed dropped to about 500 RPM the engine died at stop light. Restarted engine, but idle speed was about 500rpm, engine idle again. Ignition off/on could solve this problem temporally.
4. Dealer’s actions: adjusted some valves…(dealer didn’t descript the detailed)
5. Symptom: After dealer’s action and one hour riding, symptom is back to the same as item 1.

Owner tried TPS reset procedures - switch run, turn ignition on (but do not start), slowly twist throttle from fully closed to fully open twice, turn ignition off, the effect is the same as if just did ignition off/on only.
Dealer technician said the next action will be throttle valve assembly replacement; if didn’t work still, the following action is ECU replacement.
It will be highly appreciated if any suggestions from somebody with experiences.

[flynrider]

Hello ericlo69! Welcome to the forum.

We recently had a forum member with the problem you described in Symptom 1. His idle would go to 1500 rpm after the engine was warmed up. The problem turned out to be a faulty Idle Air Control Valve (IACV). It was replaced by the dealer.

Here is the thread :

http://cb1100forum.com/forum/showthread.php?tid=7898

[ericlo69_imp]

Hi Flynrider,
Thanks for your reply, I went through this whole "Mechanical & Technical" forum regarding idle issue before I posted this thread; however this case is pretty rare, it combine two problems together (Idle speed too high & idle speed drop). IACV is one possible root cause, and I will inform the owner for his reference. Thanks again, Flynrider.

Hello ericlo69! Welcome to the forum.

We recently had a forum member with the problem you described in Symptom 1. His idle would go to 1500 rpm after the engine was warmed up. The problem turned out to be a faulty Idle Air Control Valve (IACV). It was replaced by the dealer.

Here is the thread :

http://cb1100forum.com/forum/showthread.php?tid=7898

[kmoney_imp]

Just thinking out loud, but the problem is either the IACV not functioning or the ECU sending an improper signal (which in itself can be caused by other sensors, like engine temp sensor).

You could back probe the IACV to check for proper function (it's a stepper motor with either two solenoids or one solenoid and a spring) but this would require an oscilloscope with a graph function -- so basically dealer only for most people. All you need to see is if there is a deviation in the signal the computer sends when the bike goes into high or low idle condition.

[ericlo69_imp]

Hi kmoney,

Thanks for your precious suggestion; usually we would not have oscilloscpe on hand, however we can tell dealer your suggestion to identify the root cause. Thanks a lot.

Just thinking out loud, but the problem is either the IACV not functioning or the ECU sending an improper signal (which in itself can be caused by other sensors, like engine temp sensor).

You could back probe the IACV to check for proper function (it's a stepper motor with either two solenoids or one solenoid and a spring) but this would require an oscilloscope with a graph function -- so basically dealer only for most people. All you need to see is if there is a deviation in the signal the computer sends when the bike goes into high or low idle condition.

[Cormanus]

G'day ericlo69, and welcome. Would you please be very kind and tell us if/when the problem is diagnosed and corrected?

Thanks.

[ericlo69_imp]

Hi Cormanus,

Dealer just replaced the whole Throttle Valve Assy. yesterday; it seems the problem is solved after few hours test drive, I will keep you updated the following status.
By the way,
the dealer technicain said the IACV could not be replaced alone; it has to replace the whole throttle valve assy. We doubt this statement is true or not?
From the explored view of "Throttle Valve Assy.", there is no many electric parts, only one I see is the "Idle motor"; so I think Idle motor is most likely to be the root cause!?
Any suggestions will be highly appreciated.

G'day ericlo69, and welcome. Would you please be very kind and tell us if/when the problem is diagnosed and corrected?

Thanks.

[Cormanus]

Thanks ericlo69. I fear I'll have to leave it to others more knowledgeable about these things t comment on whether the mechanics are right or not.

Glad the problem is fixed though.

[Lord Popgun]

http://www.partsfish.com/oemparts/a/hon/...ottle-body

If you look at the parts list, it appears that the idle air control valve is referred to as the motor assm. (item 4). Notice item 8 holds it in and is the: plate, idle air control valve. The motor assm. is available as a separate part and cost ~$85. However, the Throttle Position Sensor is not available as a separate part. You can see it on the right side of the picture. OR on the left side of the throttle body as mounted on the bike.

BUT, if they order a throttle body using either item 2 or 3 it is going to come with a motor assm. and an adjusted TPS. I'll guess your techs aren't the best troubleshooters Honda has and just ordered the throttle body, when most likely it was just the IACV.

[kmoney_imp]

http://www.partsfish.com/oemparts/a/hon/...ottle-body

If you look at the parts list, it appears that the idle air control valve is referred to as the motor assm. (item 4). Notice item 8 holds it in and is the: plate, idle air control valve. The motor assm. is available as a separate part and cost ~$85. However, the Throttle Position Sensor is not available as a separate part. You can see it on the right side of the picture. OR on the left side of the throttle body as mounted on the bike.

BUT, if they order a throttle body using either item 2 or 3 it is going to come with a motor assm. and an adjusted TPS. I'll guess your techs aren't the best troubleshooters Honda has and just ordered the throttle body, when most likely it was just the IACV.

Not to cause trouble for another shop, but I would second this. There is basically no chance that a roaming idle would warrant replacement of a $2000 throttle body assembly. Even if you didn't want to diagnose anything, you would at least change and thoroughly road test the cheaper components first -- i.e., swap the IACV and ride.

If I understand correctly this was a warranty claim right? If not I'd go ask them to explain in detail what failed.