04-24-2020, 05:44 AM
Helo Speed, thanks for posting your pictures, just went over the idle speed thread and found some links that may explain what happens.
Briefly; when the key is turned on the fuel pump pressurizes for two seconds and because the ecm has no idea where the iacv is set it performs a routine to make sure the iacv is at the end of it's range of 150 steps; the iacv opens completely with 65 steps, it then closes for 35 steps depending on the engine operating temperature, these numbers may not be correct but are in the ballpark.
If you start the engine quickly when the iacv is still stepping you may find the rpm's higher without touching the throttle before settling on 1050 rpm.
During normal operation the iacv adjusts every time the throttle is operated and also tries to maintain 1050rpm in idle ( tps position ), so it moves quite a bit.
it is not obvious from your description where your reference point ( shield of the probe ) is connected, if it is connected to battery negative that may explain why it can go negative at some point, if it was connected across a coil that may result in another waveform level.
( Hi Lord popgun Sir )
If you decide to do another test with both channels of the scope be careful to not connect both ground clips to the iacv wiring, ( however using both channels you can still use batt negative for a refence and show both traces at the same time ) that could produce a fault to the iacv driver transistors or equivalent and i assume you know the basics of stepper motors.
A similar test with led's in anti-parrallel across one of the coils is here;
https://www.youtube.com/watch?v=MFA5Mk4vS3c
And another explanation is here;
http://cb1100forum.com/forum/showthread.php?tid=12203
In short; we have not found an obvious fault with the iacv valve itself but it has always fixed the problem, i suspect wear or misalignment of the piston over time, interesting post though
( edit) it may be possible to get a software update on your bike ( europe ), i think Wisedrum has some info regarding that, it is not used in the us though.
Briefly; when the key is turned on the fuel pump pressurizes for two seconds and because the ecm has no idea where the iacv is set it performs a routine to make sure the iacv is at the end of it's range of 150 steps; the iacv opens completely with 65 steps, it then closes for 35 steps depending on the engine operating temperature, these numbers may not be correct but are in the ballpark.
If you start the engine quickly when the iacv is still stepping you may find the rpm's higher without touching the throttle before settling on 1050 rpm.
During normal operation the iacv adjusts every time the throttle is operated and also tries to maintain 1050rpm in idle ( tps position ), so it moves quite a bit.
it is not obvious from your description where your reference point ( shield of the probe ) is connected, if it is connected to battery negative that may explain why it can go negative at some point, if it was connected across a coil that may result in another waveform level.
( Hi Lord popgun Sir )
If you decide to do another test with both channels of the scope be careful to not connect both ground clips to the iacv wiring, ( however using both channels you can still use batt negative for a refence and show both traces at the same time ) that could produce a fault to the iacv driver transistors or equivalent and i assume you know the basics of stepper motors.
A similar test with led's in anti-parrallel across one of the coils is here;
https://www.youtube.com/watch?v=MFA5Mk4vS3c
And another explanation is here;
http://cb1100forum.com/forum/showthread.php?tid=12203
In short; we have not found an obvious fault with the iacv valve itself but it has always fixed the problem, i suspect wear or misalignment of the piston over time, interesting post though
( edit) it may be possible to get a software update on your bike ( europe ), i think Wisedrum has some info regarding that, it is not used in the us though.