Sudden RPM surge at idle

I have looked and searched here but can't find anything that quite meets the need here. My '06 a couple years back started with this problem of when the bike is cold, when I am stopped, and when I am about to let out the clutch, there is a sudden and dramatic surge in the RMP's. Needless to say, this could have a disastrous end result. Once the bike has done it one time, that seems to be the end of the problem until the next time I fire it up after letting it get cold over night or the like. If I am not ready with the clutch, I am sure the bike will launch. That could cost the life of a child as I live in the land of the newly wed and nearly dead. (I am closing in on the latter)

A friend from out of town and I have discussed this. He suggests that it might be the o2 sensor and that this can be fixed by placing some resistor somewhere. Again, I have tried to find a thread on this to no avail. For that matter, don't even know where the o2 sensor is but I do have the manuals and will be able to find it. If this can be corrected with the inclusion of a resistor, does anyone know the value of that resistor? If I am gerry rigging something to bypass the o2 sensor, is it not correct that the o2 sensor is malfunctioning and should be replaced? Give or take, what is an o2 sensor worth anyways? I guess I can look that up myself.

I have heli-risers on the bike, but this issue started before I put them on. The heli-risers DID NOT make the problem worse. This morning, I had two episodes with this issue at different intersections at the start of my ride. Again it disappeared once the bike warmed up, so it appears this is getting worse.

Thoughts anyone?

 

Vac line leaks are often responsible for erratic idle issues. I doubt the 02 sensors could do this, as all they do is lean out the air:fuel ratio when cruising in the higher gears (they're inactive at idle).

 

Thanks for that. I will trace down the vaccum lines and try see if there is a leak there. Still, any others?

 

Have you disabled your PAIR system or anything like that?

 

This is something I have observed with my other vehicles too. My car does this too. My analogy behind this was that engine tries to run at higher RPM's initially so that it does not shut down, pretty much like what a choke does to carbureted engines. I let my engine run for a minute or two before getting the vehicle in motion.

My first motorcycle was a 125CC carbureted Honda and it did this since the day I bought it new. The colder the weather, the higher RPM's I usually saw when starting. I thought this was normal and always ignored the phenomenon. It will be interesting to see if someone has a good explanation for this. I found this thread and it has interesting answers.
https://www.reddit.com/r/explainlik...i5_why_does_my_car_idle_at_a_higher_rpm_when/

 

Pretty much all FI engines have a "cold start idle" feature (or something similar), which replicates the choke on a carb'd engine. It is temperature based and allows for cold engines to actually run properly when cold, and gets them up to operating temp faster.
The VFR uses a "wax idle unit", which retracts a little pull bar when cold, increasing the cold idle speed. That said, maybe it has something to do with the wax unit sticking... (though that seems unlikely, since a sudden release of the push-rod while warming up would cause a drop in engine speed, not a sudden increase.

 

Not that I am aware of. I've owned this bike since new in the crate, 193,000 km ago. I have read thread titles about pairing and admit, I don't know anything about that. I will have to go back and read up on it. The only thing I know about pairing involves socks or blue tooth devices. I'm good with the socks, mediocre with the blue tooth stuff.

 

I thought about this before. But when I start the bike up, the idle remains within acceptable levels, and does so even when I let it sit for a few moments in the driveway before I ride off, which I admit, is not often. Even when I come to the stop and awaited the opportunity to carry on, the idle remains proper. It is not until I begin to release the clutch that I get this sudden and massive spike. But thanks.

 

Does it do it only when it is in gear? Pulling the clutch in and letting it out in Neutral have any effect?

The reason I ask is my '14 has a feature in the ECM where the RPM increases SLIGHTY when in gear, just as I am letting out the clutch. Can not remember if my '03 6th gen did that too..

 

I don't know? I have only noticed it while in first gear but tomorrow, I will give it a few tries in neutral see what happens. As soon as I pull the clutch lever in, the RPM's drop to normal and I can let the clutch out and take off normally.

 

I have a friend like that. Every time his left hand opens, his right hand twists. He sure loves doing wheelies.

 

I can sit at a light, let the clutch out a little and see the rpms go up, the pull the clutch in and hear them drop, does this all the time. It may or may not be related to your problem.

 

Randy, if this only happens when cold, and then only once, then I think the wax unit sticking would have to a be a likely cause.

What exactly do you mean by a dramatic surge in revs? 1000? 10000?

AFAIK the only thing that controls engine idle RPM is the airflow, and that is controlled by either your right wrist or the starter valves (unless there is a random vacuum leak).

 

I have no idea Randy. But to (possibly) address your question about the 02 sensors: On my 5th Gen (2000) which did have the catalytic converter, the 02 sensors would be bypassed by installing a 200ohm resistor. But again, I don't know if your model was the same as ours.

The connection could be found on the left side of the bike. Here's a pic from the 5th Gen.

 

A charge buildup and discharge can explain one time, unpredictable events, and the clutch interacts with the electrical system at the clutch switch. Maybe the clutch switch or a component in line with the clutch switch is building up a charge, and this energy is discharged when you release the clutch and the switch is opened. This spike causes errata elsewhere in the system resulting in the RPM spike.

If this crazy theory were to have any merit whatsoever, I would only then be torn between the primary suspects of the switch vs. a corroded common ground that the switch may be connected to.

Does the clutch switch buzz? They last a few years then buzz, giving an audible sign that something is wrong.

 

Not exactly "errata" but it seems your malfunctioning clutch switch in fact is sending incorrect information direct to the fueling system, at least according to a post here:

http://www.vfrdiscussion.com/forum/index.php/topic/71888-clutch-switch-what-does-this-do/


"On a 6th Gen(at least the early ones)the clutch switch also tells the ecu the clutch is pulled in and has some impact on fueling. Sometime at a light, let the clutch out slightly and watch the rpms come up a bit. Pull it back in fully and the rpms drop. Another interesting clutch switch phenomon, rolling at speed, pull the clutch in but just short of engaging the switch, and rev the engine. The engine will shut off like a light switch - at least on my 02 and 03. Evidently if the rpms go up but the speed doesn't increase(clutch out and in gear)the ecu assumes there is a problem and shuts down. The interactions between the systems on these bikes are facinating - I just wish there was a functional description of all the ecus actions. "

 

But don't they also work at cold temperatures effecting idle speed until warm? I'm pretty sure they do.

No Power Commander Randy?

 

+1 on the wax unit, sounds like the culprit.

Video on how it works:

http://www.vfrdiscussion.com/forum/index.php/topic/59508-how-the-fast-idle-wax-unit-works/

My manual for my '14 VFR calls it an IAC Thermal valve.

 

That is interesting. Only thing is though, when my issue shows up, the rpm's momentarily jump very high. I have never really looked at the tach when this happens as I cannot predict exactly when this will happen other than sometime during the first 5 minutes or riding or so, if I stop and restart. But I will look there too.

Thank you.

 

Nope. No such beast on mine.