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Searching for a gremlin?

bowman.justin77

Member
Member
I have a 2013 C 14, and I’ve done some recent upgrades to you. The bike has picked up a weird habit of idling extremely low when cold. It will start up and barely idle at 600 or so RPM. After a few miles of riding in a come to a stop, the idle is about 1200 RPM. I am wondering if anyone has any insight as to why it would idle low, after sitting overnight, then after it warms up it idles normally. Looking for some insight as to where I start looking for the potential cause. Thank you all for your insights and feedback, this is a great group with extensive knowledge.
 

GRR125

Member
Member
The factory service manual states the following:
"Much of the DFI system troubleshooting work consists of confirming continuity of the wiring"
It goes on - later - to list at least 10 possible sources (components) that should be checked as a possible cause of unstable or rough idling. The list includes air & water temp sensors, fuel and atmosphere pressure sensors and various mechanical (position) sensors.
I'd start with the manual.
Or, you could reverse each of the recent upgrades to see if any are the culprit.
 

2andblue

Member
Member
Justin what upgrades have you done - anything recently that would muck with vacuum? How many miles on the bike? Ever change the fuel filter? Last air filter change? Any other changes or performance issues?
 

Bagger John

Member
Member
How many miles on the bike since the last valve adjustment/throttle body sync performed?

ETA:

When did you begin to notice the issue? Did it come on gradually or start all at once?

FWIW, my '12 (15k mi) does this when cold but after a warmup period that gets 1 bar showing on the temp gauge, the idle speed picks up to 1k.
 

nickrides

Member
Member
I'd bet a fiver it's the water temp sensor.
When mine firsts starts it smells a bit rich, does yours? Then goes away as it should.
Nick
2014 C-14
 

bowman.justin77

Member
Member
Justin what upgrades have you done - anything recently that would muck with vacuum? How many miles on the bike? Ever change the fuel filter? Last air filter change? Any other changes or performance issues?
Nothing that would mess with vacuum, 32k miles, last Major service was 17k miles. I am scheduled to have it done again in December.
 

Fred H.

Administrator
Member
Cold idle speed is not controlled by engine vacuum. It is instead controlled by the cam on the left end of the throttle bodies. The secondary butterfly servo is utilized (by the ECU) to adjust the cam position and control cold idle speeds. Once the engine temp picks up a bit, the servo returns the cam to the normal idle position.

If you have installed a cruise control and connected it to the throttle pulley, make sure it isn't interfering with the action of the throttle and cam for the cold idle. Also, make sure your throttle isn't binding in any way. The cam needs to be able to roll the throttle a bit to pick up engine speed. When the engine is still cold and the cold idle cam is in play, you can actually force the idle speed to slow down by manually forcing the throttle closed when the engine is cold and you should hear the engine speed drop. If you release the throttle it should then pick back up in speed.

Also worth mentioning, if incorrect mapping is done on a ECU reflash for the secondary butterflies, it can nullify the cold idle speed control.
 

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IBAJIM

Member
Member
Nice video Fred ! I wondered how that worked.

I would try hitting that area on the left with some carb spray clean and see how easy it is to move that cam before & after I did that. And check the electrical connection to the "servo" motor ( probably a stepper motor ) on the right hand side of the throttle bodies.
And it looks to me like that screw adjustment on the left side determines the cold idle speed when the bike is first started when cold.
 

Fred H.

Administrator
Member
Since the cam is tied to the secondary throttle butterfly shaft, it if isn't turning for any reason, you'll get an FI code set because the position is monitored by a throttle position sensor. And yes, it is a stepper motor that controls the butterflies, I believe it's a 4 wire stepper motor.
 
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