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Discussion Starter #1 (Edited)
Hi all, first time post,

Just for specs. I own a VN900 2009 Special Edition, V&H slash cut exhaust with K&N air filter. No other modifications.

So onto the problem.

On very intermittent occasions when cold starting the motorcycle, it starts, fast idles (if needed) clicks into gear and away I go, give it about 20 seconds of riding and if I pull the clutch in to stop, the bike idles VERY rough and has sometimes stalled.

What makes it even "odder" is that if I feel the idle getting rough in gear with the clutch pulled in, and I change into neutral, let it sit for 5-10 seconds, the fast idle kicks in once again and it idles fine. If I don't change into neutral, it'll run rough when pulling in the clutch coming to a stop until the bike warms up.

At the moment it's not an issue that is making the bike unuseable, but it sounds like some type of fuel regulation/fast idle issue?

Any ideas?

Cheers all!

To note here in the UK we have alot of sh**** weather, and water getting into connectors could be an issue as I have already had to put dielectric grease on the oil pressure sensor due to the oil light flicking on when raining. Could it be something similar to this? I'm riding this thing in any weather including some days where I feel like I'm in a monsoon
 

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I'm not sure if this will help, but when I start my 900, I let the fast idle warm up the bike first (dropping back to normal idle), before I put it in gear and take off. I always found it a bit weird trying to ride the bike while adjusting to the temporary fast idle engine speed. I prefer normal idle while riding, and I only have to wait a couple of minutes (a bit longer in the winter), before I take off.
 

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@Cal52413
that's a nice touch with the dielectric grease on the oil pressure sensor. I also sealed the whole assembly with some silicone as I recall...

So being in gear or in neutral is what makes the difference.
To me that sounds more like electronics related than mechanical.

What RPM does it idle at when warm?

(this is how 1000RPM sounds like, I have noticed some people set the idle lower [too low] just to mimic a long stroke V-twin sound.
)
 

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Discussion Starter #4
Cheers for the replies, yea it's idle sounds pretty much on par with the video and isn't too low.

See that's what I thought, got to be something electrical as being in neutral is almost like "tricking it" to come on. Taking a completely mad punt/guess here but could it be the reg/rec as this is quite close to the front and could be letting in water too? I know it's mainly concerned with battery charging and converting current but could a bad one cause abnormal behaviour?

Cheers all
 

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Cal52413, does your bike have O2 sensors? The reason I ask is because of the bike's behavour. With O2 sensors, your bike will switch between open and closed loop function. I'm guessing at this, but closed loop (using feedback from the O2 sensors), requires heat for the O2 sensors to work properly. When you stop at a light for example, the bike will idle for a brief time closed loop, then switch to open loop (without the O2 sensors) to a standard fuel map, as the sensors cool at idle.

It sounds to me like the O2 sensors (or the connections to them) are not conducting voltages properly. Do you have an error code from the ECU?
 

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Did more research looking at the service manual. The O2 sensors have heaters, as most modern O2 sensors do. Does the FI light come on? If it does not, then it's possible that the O2 sensors work properly when heated by the exhaust, and thus the ECU sees them are working correctly. However, it's possible that one of them has a failed heater, that causes the O2 sensor to stop working when it cools down. Again, I'm just guessing, but the switch from rough idle to smooth idle at a stop light, suggests a mode switch by the ECU, that seems related to the O2 sensors. The service manual recommends tests to verify correct operation of the O2 sensor and the sensor heater.
 
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