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CB1100 Idle speed instability problem
Hello all,

It's with a heavy heart I write this comment but I'm at my wit's end trying to tackle this solo so far! I believe my 2017 has been afflicted by this nasty IACV issue and it's a real bummer, but it's taken a long time to diagnose because of how intermittent it is. I had put about 22,000 miles on the bike before I had the valves adjusted (not that I noticed any issues, but I felt like it was overdue). While I had that done, I also got my bike professionally tuned by a local shop with a good reputation. Although it rode fine for a while after, things have gotten progressively worse and I think I'm going to have to take the bike in soon.

First, I had very intermittently had issues with high idle as I started the bike (~1800rpm) until it was warmed up, and those were solved with a kill-switch reset. I paid it no mind, really, since it happened like 3 times over the year I was riding it and solved itself generally.

Then I started noticing it would stay above ~1100 rpm even after it should have warmed up and this happened frequently.

THEN I noticed that the RPM would drop to 5-600rpm at idle, rolling up to stop signs and in traffic, and unless I rolled on the throttle immediately, it would die. It would start right up on me, but would die at the next stop sign.

At this point, I tried to remedy the issue myself. I changed the oil and filter early (usually at 5,000mi), spark plugs, cleaned the air filter, cleaned the TPS sensor and checked for kinks, reset the TPS, and while I was at it changed the brake and clutch fluids and replaced the chain and sprockets. I also tried to give it the ol' Italian tune-up, riding with very high RPMs and redlining it for a bit. I tried to seafoam the oil and gas and emptied and refilled the gas tank as well. I tried a tank of 93 instead of the usual regular I use. I would test after each of those fixes and was still having trouble, but eventually it just sorta stopped happening.

The idle at start was high, 14-1500 until warm, but after about 10 minutes of riding it would settle at around 9500 and was *fairly* stable. Less stable than I was used to before all this, and not reading where it should, but it got me around town and felt great when I was in motion. And for about 1000 miles it didn't die on me again, but the weather was getting cooler too at this point and I hear ambient temperature could affect the IACV issues.

So yesterday it was a warm LA day and I went for a ride, it died on me a few times in traffic. Same 600rpm to stall pattern as before.

So the question I have is this: does this sound like IACV troubles? Anything else I can do? Money isn't exactly flowing like water with COVID so if I could avoid giving a shop several thousand dollars to fix a highly intermittent and difficult-to-diagnose problem that'd be great.
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RE: CB1100 Idle speed instability problem - by iamheero_imp - 12-10-2020, 04:08 PM

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