03-12-2018, 07:15 AM
Just wanted to add my experience here. Same issue with idle rising when letting out the clutch in gear, but before any meaningful engagement. Also, the idle would typically rise just by putting the bike in gear, and holding the clutch in the same position (completely disengaged).
In my case, yes I noticed a material increase in fuel consumption. My bike doesn't seem to do well in terms of fuel usage anyway (<40 MPG around town), but I was getting LFL before 90 miles in some cases with the high idle. Also threw off a lot of heat.
(03-12-2018, 05:45 AM)max_imp Wrote: Nice job mechanix, no doubt about the validity of the test, it proves the switch IS providing the input ( b22 sstand ) to the ecm, disconnecting it without even touching the lever causes the increased idle.
So why does it do that and is it a fault with the wiring?
+1 on sportsterdoc on the internal programming of the ecm, combined with bindir's findings i would agree that is the case, never noticed it before? could have easily missed it with all the enjoyment that riding such a nice cb1100 brings.
If it was a fault in the wiring it would persist when the bike is cold or warm, it does not do this and therefore unlikely to be a faulty ground, but still worth checking for corrosion etc.
If the negative battery cable has a bad connection it would quickly show up in a bad starting and dimming of the instrument cluster on application of the start switch at which point 150 amps flows through the cable and loosing 2 volts at this point could mean the difference between a good start and no start, this 2 volts would be 0.1 volt when the battery charges with 7 amps but would not have an effect because the sensor grounds come together on the frame at central points, engineers have discovered this ground pitfall and grouped the wiring accordingly ( check the wiring diagram ).
By the way i use my green neutral light as a battery tester, it dims as the bike starts, the more it dims the lower the battery capacity is, 2010 model.
So i would like to think of this as an undocumented feature honda has knitted into the later models to "assist" drivers in adverse conditions, ( but just never heard of this bahaviour and stand corrected/ like to hear from others as it could be a clue ) they just forgot to tell it to the printers of the manual.
Thinking about your explanation that this increased idle switch behaviour lasts for 4 miles longer than the original cold idle does make me think though, as far as i can work out the engine temp is sensed by the Engine Oil Temperature sensor below the throttle body, the other temp sensor is in the air intake after the air filter in the velocity stack chamber, but that should not change because it measures ambient temperature which does not change when the bike is driving.
From the video it appears that the iacv works fine and consistent in this part of it's travel range, it may be different in another part, though.
Briefly ; on startup the iacv is "reset" to the end of travel ( open, position 120 ) and then stepped to the cold position ( position 85 ) and gradually moves to it's operating position ( around 70 ) to maintain 1050 rpm, these are approx values to illustrate what happens, and conventional thinking is that the iacv has a problem around position 70 ( thanks popgun ) and produces the idle issue for reasons we are still trying to work out, it is quite hot in there during slow traffic and among other things may affect the magnetism in the permanent magnets in the rotor section of the iacv, weakening them, again ; speculation from me at this point
Have you noticed an increase in fuel consumption? that appears to be one of the symptoms associated with low idle syndrome.
Good video; max
In my case, yes I noticed a material increase in fuel consumption. My bike doesn't seem to do well in terms of fuel usage anyway (<40 MPG around town), but I was getting LFL before 90 miles in some cases with the high idle. Also threw off a lot of heat.