CB1100 Idle speed instability problem

[kennyw]

Thanks curleyjoe. I understand that the IACV is not subjected to fuel, but the valve itself (it's electro-mechanical) could be sticking. Also, the valve could be sticking in the throttle body interface due to an imperfect fit. I can understand how a sticking valve can cause symptoms that come and go, but I don't understand how unplugging my EOT sensor suddenly makes the bike run perfect. Maybe unplugging the EOT sensor causes a completely different signal to be sent to the IACV that forces the IACV to react in a way that cures the unstable idle speed? Maybe this forces the IACV to go into a fully closed or fully open position that overrides a sticking condition? I have always used top-tier, 91 octane fuel in my bike, but that doesn't mean I didn't get some bad gas at one time. I wish I had more feedback concerning the effect on the high RPM idle when unplugging the EOT sensor. I believe somebody posted that replacing their EOT sensor cured the problem - replacing mine did not. To be continued.

Recycling engine blow-by gasses back into the intake may help the environment/emissions, but is lousy for the engine. Just ask any owner of a diesel pickup built in the last few years....

VW diesels had an issue with this in the early eighties. The blow-by gasses caused the engines to accelerate unexpectedly.

My guess is you are triggering a limp mode by unplugging a sensor input that the computer needs. Limp modes do not automatically try to adjust on the fly. However, that is pure speculation as i have not studied the system.