CB1100 Idle speed instability problem

[dave]

Dave, sadly there’s no way I can answer the question you pose, but I did want to tell you I’m full of admiration for your incredible persistence chasing down a solution to this problem.

Hi Cormanus, thank you very much. I have to thank all the great people on this forum who have encouraged and supported me the whole way. The job is only half way done now, and I am praying that the new IACV will cure this idle problem.
Q1; was the iacv disconnected when you removed it? picking it was connected.

It was disconnected for the last 50 miles I rode the bike, with slow idle on start-up, and perfect idle with the engine warmed up.

q2; now that they are both out is there a difference in binding the threaded part i.o.w. does the old one run freely?

No. Both valves thread very smoothly the full range of travel on the threaded shaft.

a1; position of the piston inside; it has worked fine before all the trouble started so unless the ecm has slowly dribbled out of position ( stuck during part of the travel and still counted the same amount of steps ) i expect it to be correct.

This is a possibility. I posted a while back that the sound I heard when I first turned the key on became noticeably louder on one occasion. It could have been the IACV noise, but then again it may have been the fuel pump.

As far as i can work it out it chases a moving setpoint depending on air and engine temperatures so it should have a tendency to "shuffle"along the working part of the cylinder and resets to a pre- determined position every time the engine is started from cold.
In other words it automatically finds it's own spot.

Question: If it finds its own spot, can it automatically compensate if it is installed incorrectly - ie, if the valve is not threaded completely to the bottom of the threads on installation?

The concern i had was if the piston was initially mounted too far into the barrel ( not wound back ) and the thread was compressed against the end of the barrel where it has a minimal amount of threads on initialisation.

I think the real answer is that you would need an obd2 tool to tell exactly where the piston is at any time, however we know that it is not in the target position if the engine idles badly, so you can reliably guess when it is too far open or closed.
( if you can see the shadow of a tree you know the tree is there otherwise what makes the shadow?)

a 2; if the iacv was connected and the bike idled ok prior to being switched off the iacv was indeed in the correct operating position for a warmed up engine, well done Dave.

The bike idled fine when warned-up, with the IACV disconnected (which it was for about the last 50 miles, and three around town trips). Do you think it's possible that the valve somehow moved (vibration?) during the 50 miles I traveled with it disconnected? I am guessing that it would not.

Could it be that the valve was on an angle in the barrel? ( Minor scuff marks at the very end of the tip of the piston )

I don't believe so. There is no visible indication of any kind f damage or scuff marks, and the valve removed effortlessly from the cylinder, indicating no binding at all.


Can we have a look at pictures of both iacv's prior to mounting the new one?
[/quote]
I will provide pictures, but you won't see any difference between the two valves.

My next step will be to reinstall the battery and test both old and new IACVs side-by-side. I hope they will work - I have disconnected many wires that I don't know if this will have any effect. I did inspect the new IACV prior to any disassembly and it appeared to function properly (to the best of my knowledge, anyway). I can only compare the old to the new to see if there is a difference.