How does the return to idle works on Kehin anyway - Page 2 - Triumph Forum: Triumph Rat Motorcycle Forums
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post #11 of 14 (permalink) Old 12-04-2012, 03:57 PM
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You said that you solved the stalling so what is the "low idle speed issue"? Is the speed constant but too low or does it go up and down?

I really donít have any good suggestions about a possible cause so you just have to work through a few things to see if you can narrow it down.

Originally Posted by Sparkydany View Post
When the ignition is off, the idle stepper motor's control lever arm is touching the throttle cam.... Maybe that could explain my issue.
No, I don't think so. The fact that they are touching does raise a question but you're getting the correct TPS voltages so it's way down the priority list even if we can't rule it out completely. It's possible that the ISC stepper is sticking but you got the correct TPS readings so I think there's only a slim chance.

Originally Posted by Sparkydany View Post
Ö.before starting the bike, the coolant temp was showing 3 Deg C while the air intake temp was showing 10 Deg C. Ö.ambiant temp was indeed around 3 - 4 Deg C.
OK, this grabbed my attention. I agree, it doesnít sound right. The problem with this one is I canít imagine such a small difference in IAT would affect idle speed. IAT combined with baro pressure is used by the ECM to adjust for air density (due to changing weather/altitude). A 7ļC change in temp would not have a major effect on air density and the amount of fuel delivered. Also, I would expect the idle speed control to compensate. Idle speed is determined by temperature but that would be linked to coolant temperature which seems to be OK since itís the same as ambient temp before the bike is started. I donít really have any other ideas right now so that seems like a good place to start.

The Inlet Air Temperature Sensor looks like a possible culprit. You didnít mention a MIL light or any error codes so it doesnít appear to be a failure but it could be out of range without giving an error code. With the tank off the bike itís easy to check. Simply pull the plug from the IAT sensor (located on the airbox lid) and measure the resistance across the two pins. Compare with the values in the maintenance manual. The values will change according to temperature so you may need to find a method to heat or cool the IAT. You could also run the bike with the IAT disconnected just to see if that affects idle speed. Youíll get a MIL light and error code (P0113) but you can clear those with TuneECU when youíre finished.

Originally Posted by Sparkydany View Post
Throttle are balanced, checked.
See fredsprint's comments in this thread. Do you know where the throttle balance screws are set at? From my own experience adjusting the screws from Ĺ turn to 2Ĺ made no difference as long as balance was maintained. If you open or close the screws to allow more or less bypass air then the stepper simply adjusts throttle position to compensate and maintain idle speed. However, fredsprint did notice a change with his friend's bike so we have to keep in mind that it can affect some bikes. Maybe if the stepper is slow to adjust then you could experience stalling but so long as it doesn't stall it should settle at the correct idle speed.

It's amazing how fast you can go when you take your time.
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post #12 of 14 (permalink) Old 12-04-2012, 10:37 PM
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Hi Champ. Thanks for taking the time to answer.

Sorry, i did not detail my idle speed issue in my post.

The stalling issue did not come back after i fixed the cracked rubber boot and the loose throttle clamp. My idle issue is that once in a while, when downshifting to a complete stop, when the clutch is pulled and the bike is in first gear, the idle speed will go down in the 10500 -1100 RPM range. Most of the times, when it occurs, the idle will stay in the low 1100 RPM. Not a big difference from the 1170 - 1200 target idle speed but it is still bothering me.

I could never link this issue to weather, engine temp or anything else. Simply no trend. Never had a MIL light displayed nor fault codes stored in the ECM since i bought the bike.

As you recommended, i will check the IAT (and coolant temp) sensor. I am curious to see where the 7 Deg split comes from. It could be a wiring issue adding an intermittent offset to the output of those sensors.

Finally, i am also thinking buying a used throttle body assembly and replaced the Stepper motor and TPS sensor. This way i could clear those possibilities.

Thanks again for your time. I am learning a lot reading you guys. I will advise if i ever find the culprit.
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post #13 of 14 (permalink) Old 12-05-2012, 06:39 AM Thread Starter
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figures are:
warm: 200~400 Ohms
20įC:2.35 ~ 2.65 kOhms
-10 įC: 8.5 ~ 10.25 kOhms

So its a negative coeff thermistor. Then if you get additional resistor due to bad contacts you get a lower temp reading than the real temp. So you're on the good way.

But a lower temps reading would get the idle higher, not lower in regard to the idle/temps table. Maybe the fact it's erratic could cause problems.


Last edited by fredsprint; 12-05-2012 at 06:42 AM.
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post #14 of 14 (permalink) Old 12-06-2012, 11:42 PM
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Hi FredSprint,

Thanks for the info. The resistance values will be useful. I'll keep investigating and i will post any results.
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