CB1100 Idle speed instability problem

[dave]

Update: Tightening the loose throttlebody connection clamps does not cure the low idle problem. Here’s a description of my experience with the low idle condition returning last evening. The temperature was in the low 60’s. Bike started normally, and I proceeded 1 mile to the freeway, stopping at two stop lights, where the idle was normal. Proceeded 28 miles on the freeway, averaging 70 mph, and exited. Immediately at the first stop light the idle dropped to 700 RPM, and worked its back up to approximately 1,000 RPM. I proceeded about 2 miles to my destination, stopping at 4 more stop lights and each time he 700 RPM condition returned. When I reached my destination I put the bike in neutral and revved the engine several times; each time the 700 RPM condition returned. I turned the engine off with the key, restarted it, and no change. I turned the engine off again; turned the key to “on” and performed the TPS reset procedure, and then turned the key off. I restarted the bike and it was running perfectly. Note: I have performed this exact same TPS reset procedure several times in the past when the low idle condition occurred and it never worked before. The bike sat for approximately 2 hours before I restarted it for my return trip. It started normally, and idled fine at the first stop, approximately 100 yards away. Stopping at the next light, approximately 200 yards away, the low idle condition returned. I put the bike in neutral and revved it several times with no change, except this time it stalled once. I performed the TPS reset as described above and the problem was cured. I proceeded to the freeway and stopped at three more lights, where the idle was fine. The temperature was now in the mid 50’s, and I rode the freeway 28 miles, averaging 70 mph. Exiting the freeway and at the first 2 stop lights the idle dipped lower than normal, but not to 700 RPM, and worked its way back up. When I reached home, 1 mile from the freeway, the 700 RPM condition returned. I again revved the engine in neutral, with no change in idle speed. In my opinion, when the low idle condition returns the engine seems to be running lean, because it does not respond to throttle input as readily. I turned the engine off with the key and restarted it with no change. I performed the TPS reset described above and the low idle condition was cured. I next turned the engine off and unplugged the TPS, and restarted it. I was idling at approximately 1,000 RPM, but throttle response was weak, very similar to the response when the low idle condition was present. I revved the engine several times with the TPS unconnected, and it would return to approximately 1,000 RPM each time, but the throttle response remained weak. (The check engine light was illuminated.) I turned the engine off and plugged the TPS back in and restarted it, and it was running perfectly again. There was a very obvious difference in throttle response from when the TPS was disconnected. I revved the motor several times, and each time it returned to a perfect 1,050 RPM. I turned the engine off and parked the bike. Note: When the low idle condition returns the engine speed drops much quicker than normal, which I noticed especially when shifting gears because the immediate drop to low RPM when shifting causes noisy shifts, caused by the chain slack loosening and tightening. So in summary, tightening the loose throttlebody clamps does not cure the low idle condition.