CB1100 Idle speed instability problem

[dave]

Update: I cleaned the electrical connection to the air temperature sensor. The connectors all looked good when I unplugged it, but I sprayed everything with electrical cleaner and blew it clean with compressed air. I started the bike with the air temperature sensor disconnected and it seemed to start and run normally, except the low/cold idle speed was lower than normal, at about 1,100 – 1,200 RPM. The engine was cold, and the outside air temperature was in the upper 50’s. I only let it run for about a minute as I blipped the throttle a few times, and the idle decreased to about 1,000 RPM before I turned it off. I disconnected a three-pole connector directly in front of the air temperature sensor connector to try an gain more room. This connector was attached to a clip on the frame and it was not coming off (my bike looks different than the middle of the three illustrations on page 5-76 of the FSM, but I believe this connector was the one in the picture with the text [3]/[4] just above it). I immediately took the bike for a test ride, going about 8 miles with a mixture of freeway and city streets, turning the engine off and restarting it twice. To my surprise the bike ran perfectly. So I took the bike for another test ride last night, this time slightly longer. The temperature was in the upper 50’s again. It started out running perfectly, but after about 10 miles the low idle condition returned. I rode home, where the engine stalled in my driveway as I gently blipped the throttle a few times. So in summary, cleaning the air temperature sensor connection did not cure the low idle problem.

I was planning to clean the connector to the MAP sensor next, but after reading the FSM to learn where it resides I have decided to skip this test because it is almost as easy to just replace the IAC valve. I’ll clean the connection to the EVAP purge valve next, but if this doesn’t work I am just going to replace the IAC valve.