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Revs going up to 3-4k soon after cold start


Tom
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Noticed this few days ago. Bike starts up normally on cold starts, float around 1300 or something, but as soon as I'd move out of the garage to the first junction, that's half minute of distance, when I'd put the bike in neutral I saw the bike having higher revs in idle.

 

And I think it would initially stay at whatever my "last" throttle was before pulling the clutch. I would put the bike in neutral, saw the tacho at 2000 rpm which immediately caught my eye (and ear) and then blipped the throttle slowly to lets say 3000 rpm - release the throttle but the rpm's would stay at 3000 and would creep up, but very very slowly. 

 

Then, engaging back the gear and moving down the road, if I'd let the bike move without any throttle - the bike would barely roll forward. I thought that high idle would act as "false throttle" when no actual throttle was applied on the grip, but that wasn't the case, when in gear, no throttle meant no throttle. The problem would occur for maybe a minute (bike would be well into operating temp) and then everything back to normal, neutral gear normal idle speed etc.

 

Where do I start looking? (2002 Bird)

Edited by Tom
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I'll look into it at my friends garage in a couple of days. Vacuum leak "should" be on the lines under the tank only, no other place right? 

 

And I'll give the temp sensor a test, that's the one on the left back side of the rad?

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9 hours ago, XXitanium said:

More info.

 

No mention of fast idle in that thread, which part specifically should I take note of, MAP sensor vacuum hose?

 

4 hours ago, XXBirdSlapper said:

Throttle cable being pulled due to interference

 

I will say that I have tinkered with the cables in a very shoddy way - but this was few months ago. I tried to remove the right side handlebar switch and I wasn't able to remove the end weight (screw kept turning in place, nothing happened) so I split opened the switch and tried to maneuver the cables out of their position in the grip, but there wasn't enough slack to do it - or I wasn't skilled enough, could be the reason as well very likely :)

 

So I put everything back and for a couple of months everything seemed normal.

 

In the meantime I did buy those inner clips or whatever they're called on the grips, because I think my previous mechanic might've over-tightened the weights and now I can't get one of them out. We'll see, I'll be taking care of it these days, just hope it's not something serious.

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Did you try pushing the throttle toward idle or just released it?  If you pushed it and the RPM stayed up then it's less likely to be a cable problem, and a cable problem is unlikely to only happen during warm-up and then cure itself.  I think trying that should be first on the list toward diagnosing the problem.

 

I recall my '01 having a slight idle change when actuating the clutch lever.  Engaging the clutch safety switch was apparently triggering a change from the ECU, but I don't know what or why.  There's apparently a mystery connection there that could maybe lead to erratic behavior.  I say "mystery" because I've never seen anyone talk about it.

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Went for a ride today to do some errands, and as soon I got out of the garage I had a green light streak thru the city so by the time I got to my parking lot, the bike presumably got "over" its idle bug and this time I didn't see it happening. And I had to postpone the visit to the garage, but will update when I get to it.

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For FI Birds, there is a mechanism on the throttle bodies that defaults (cold condition) to a fast-idle, and then when the coolant gets warm, it goes to a normal idle.  That mechanism may be "sticking", the wax inside the actuator may be leaking/going bad, or the flow of coolant through the tiny hoses may be impeded or blocked.  Once all that stuff gets some heat from the engine and exhaust pipes, it's magically fixed.  Coolant flow blockage is the most likely.

This is something very rare, but figured I would through it out there.  I'm always late to the party, so the common/simple stuff has already been mentioned.

Good luck.

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1 hour ago, jon haney said:

For FI Birds, there is a mechanism on the throttle bodies that defaults (cold condition) to a fast-idle, and then when the coolant gets warm, it goes to a normal idle.  That mechanism may be "sticking", the wax inside the actuator may be leaking/going bad, or the flow of coolant through the tiny hoses may be impeded or blocked.  Once all that stuff gets some heat from the engine and exhaust pipes, it's magically fixed.  Coolant flow blockage is the most likely.

This is something very rare, but figured I would through it out there.  I'm always late to the party, so the common/simple stuff has already been mentioned.

Good luck.

Plus 1.

Btw, check coolant level. If it's too low it could cause symptoms like that. 

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2 hours ago, jon haney said:

For FI Birds, there is a mechanism on the throttle bodies that defaults (cold condition) to a fast-idle, and then when the coolant gets warm, it goes to a normal idle.  That mechanism may be "sticking", the wax inside the actuator may be leaking/going bad, or the flow of coolant through the tiny hoses may be impeded or blocked.  Once all that stuff gets some heat from the engine and exhaust pipes, it's magically fixed.  Coolant flow blockage is the most likely.

This is something very rare, but figured I would through it out there.  I'm always late to the party, so the common/simple stuff has already been mentioned.

Good luck.

 

This reminded me that it happened to a friend's bike.  I think maybe the was leaked or something?  Dunno, long time ago, but he bought a new one.

 

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Well this does sound like a logical reason and it might as well be coolant flow related - which then makes me think why am I losing coolant in the first place. Winter service is due, I bet I'll be in for many surprises.

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8 hours ago, Tom said:

Well this does sound like a logical reason and it might as well be coolant flow related - which then makes me think why am I losing coolant in the first place. Winter service is due, I bet I'll be in for many surprises.

It's way too early to jump to that conclusion, but it's something pretty easy to check.

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On 11/29/2022 at 5:43 AM, XXitanium said:

I was thinking the FI flashes/ codes might help. I don't recall a fast idle problem being discussed here before.

Waste of time. Idle speed control on fuel injected XX is purely mechanical. I mean there is obviously cold coolant temp mixture correction map but that would not cause 4000 rpm idle speed.

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6 hours ago, tomek said:

Waste of time. Idle speed control on fuel injected XX is purely mechanical. I mean there is obviously cold coolant temp mixture correction map but that would not cause 4000 rpm idle speed.

Don't see where he said 4000 RPM.  That would be too high even for a malfunctioning fast idle circuit.

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4 hours ago, jon haney said:

Don't see where he said 4000 RPM.  That would be too high even for a malfunctioning fast idle circuit.

Title of this thread. 

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  • 3 weeks later...

Well, went for a Christmas shopping around town today, wasn't on a bike for week or two, so stone cold...started normally, idle sounded normal, then instead of what I suspected (revs creeping higher up) it started to slug down slower and slower, and then the bike died.

 

Started it again, revs now very low and after few seconds no revs at all again haha, and then I started it again and held on throttle for few seconds, and it seemed to work. I'll order the wax unit right now :D

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you can test the wax unit on your bike by starting the bike while cold and seeing if it moves.otherwise just remove the wax unit and heat it up from cold and see if the rod moves.no idea what he is saying but you get the idea   

 

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On 12/19/2022 at 5:47 PM, XXitanium said:

@jon haney ?

 

I assume you are referencing the photo Tom posted, but I can't open it on my work computer, and I can't use my cell phone in our building due to very weak signal. 

Edited by jon haney
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