CB1100 Idle speed instability problem

[SportsterDoc]

Nice one Dave, steady idle during the last test and not even in limp mode either?

Thinking what could go wrong in assembly; the throttle body would be assembled in one piece away from the bike and later mounted to the engine before insertion into the frame.

Have they screwed the piston in completely before inserting the iacv into it's cavity,
Is the shaft straight before mounting, was a box dropped before assembly?
Was the iacv screwed in on one side first and damaged the piston/shaft?
Has someone not lubricated some parts or used the wrong lube?

Guess you will be the first one to know what made the detective story happen in the first place.

So one thing that would be interesting for the future is if you have the old iacv unplugged just like now see if you can plug the new one in and fool the ecm so that it thinks the iacv is still connected ( no check engine light ) and see if that makes a difference in the way it drives as you mentioned there seems less power, this can still be done once the new one is in place, and as a bonus you get to see how the iacv operates on startup and during a ride.

We would all like to see pictures side by side of the iacv's as it came out of the tb and it would be a good idea to measure the distance the piston is extended from the iacv body so we have a record in which part of the travel we can expect erratic behaviour.

And if you can make a video of the same side by side showing them 360 degrees closeup and sharp maybe we can get a better idea what the problem was, Magnus's pictures were good but better resolution and more of them would be very nice for the future and possibly convince Honda dealers why this happens.


What i expect you find is a slight binding in travel of the piston in the area when it is removed, and are any of the piston parts plastic?

Congratulations Dave!

Other than the apparent ECM program, on some bikes, which increases idle as clutch is released, it would seem that unplugging the IACV would eliminate a fast idle.

Any further comments, Max?