Sudden RPM surge at idle

Have you check your throttle body boots for tightness? They may need a turn or two to make them totally air tight.

 

Tried this several times this morning before I headed out for a ride. Could not get it to rev in neutral at all. Then again, the high rev while in gear did not happen today either, so maybe today, being Tuesday and all, was not a day for the gremlin to appear.

 

From how I understand the fast idle wax unit, when the bike is cold, this unit causes the RPMs to increase a little until the bike is warmed up. Similar to a choke. Mine does rev a little higher when cold and then drops to normal in short order. But this sudden surge is drastically higher that a light increase one would expect from this unit. The RPMs, going by the sound of the engine only, probably triples the normal idle speed if not more. I am going to have to try to watch the tach for the next while.

The clutch switch is something to consider for sure. But reading up on that, I don't really understand why a faulty switch there would cause this sudden and high surge. But, the bike is very high mileage. It is ridden in just about all elements, and used to be exposed a lot to the water and road debris of winter. So who knows.

I understand the Clutch Switch maybe a relatively cheap replacement item. Even if it is not the cause, given the mileage and age, this might be a worthwhile change anyways. When my next pension check comes, that will be ordered and the replacement done. I should be able to do that. Mind you, I did manage to strip some bolts in the past.

Failing that, it has been quite a while since a qualified tech has looked at this bike other than two stator replacements so maybe it is time. That too will have to wait until my governemtn gives me more money. Cheap thieving bastards they are.

 

I had a similar problem with my '02, where the idle would randomly jump to 4000rpm. I read through a few threads and found the wax idle unit has been implicated, under the assumption that it sticks open intermittently (causing a high idle). When one poster replaced the wax unit, he found it was stuck in the high-idle position.

Given how dangerous a random jump in idle speed could be and that the wax unit is fairly cheap ($40-50 for the part) and easy to replace (no need to remove throttle body but do need to drain coolant, should take 1-2 hours), I ended up replacing it. The problem did not reoccur after the replacement. Although I'm not a fan of diagnosis by part replacement, in this case I'd recommend trying this fix. Other people have tried lubricating the shaft of the wax idle unit.

Here are some related threads:

http://vfrworld.com/forums/showthread.php/10457-Fast-Idle-Wax-Unit-amp-Starter-Valve-Synchronizing
http://www.bikersoracle.com/vfr/forum/showthread.php?t=58986

 

Randy, you have lot of kilometers on your bike.

When was the last time you inspected and cleaned the MAF on your bike? These can cause issues similar to what you're describing at idle / low throttle - especially when the bike is cold.

A few other things to check:
- Catalytic Converter may be starting to fail / block affecting the A/F ratios and messing with the O2 sensors.
- Vacuum Leak
- Fuel Pump / Regulator / Strainer failing.

No codes in the computer are there?

 

No codes indicated ny the FI light.

@ nearfreezing. Your experience sounds very close. Except mine is less random. It only seems to happen when the bike is in first ar and I am just starting to disengage or release the clutch lever. Usually it only happens once but a few days ago, it happened twice at the same stop. Then it was fine for the rest of the day.

 

I would definitely check your MAF and try cleaning it. Cheap - all you need is a can of electrical contact cleaner.

Pull the MAF out, there should be little tiny hair like wires - they need to be cleaned as they are collecting the data. If they are dirty (and they do get dirty), they can cause all kinds of bizarre things to happen, including reduced fuel economy, poor idle, surging, etc.

One other thing to try ... check your neutral gear sensor. This can cause surging if it's intermittently going wonky.

 

I would consider the Air Idle Control Valve. It only works at Idle.
The CPU sends it a Duty Cycle'd signal that chatters the valve, to allow the right amount of air during Idle.
The connectors/wiring should be checked.
The valve air channels are probably gum'd up/clogged.
The valve asm could be past End of Life, sticking. (replace).
http://www.partzilla.com/parts/search/Honda/Motorcycle/2008/VFR800+A/AIR+INJECTION+CONTROL+VALVE/parts.html
https://www.youtube.com/watch?v=3tLtbI9OfYc

This Control Valve allows appropriate Idle at Cold Startup.
This Control Valve will provide Proper Idle at High Altitudes.
Some CPUs may post an Error Code if it asks for more Idle Speed and doesn't see it.
This Idle Control system makes for good Engine Behavior at all Temperatures and Altitudes.
This unit is Simple, very Functional and weighs almost Nothing.

 

Most 6th gen'ers just rip that crap out and block the PAIR valves to be done with it. It's useless crap that only adds weight.

 

You are mixing and matching. You referred to the PAIR (Pulsed Secondary Air Injection) valve in the parts list for the VFR but describe and link to a video of an automotive AIC valve.

The PAIR injects air into the exhaust to burn unburned fuel. It is a smog control unit devised in the 1960's. It does not control idle like the AIC.

On the VFR the starter valves control RPM from idle to 4% throttle like the AIC, they do similarly bypass the butterfly, and are controlled by the idle wax unit or a lever on the 5th gens.

 

You're right,,..

http://www.partzilla.com/parts/sear...008/VFR800+A/THROTTLE+BODY+(ASSY.)/parts.html

AIC is performed by the Wax Thingy (#3), like a Rad Fluid Thermostat. I woulda preferred a Duty Cycled Solenoid.

 

If there were air bubbles in the Fuel Rail, cylinders would drop out, maybe even stall.
If there was Over Pressure in the Fuel Rail, the engine might Surge.

http://www.partzilla.com/parts/sear...008/VFR800+A/THROTTLE+BODY+(ASSY.)/parts.html

Fuel Rail Regulator (#19) may be sticking? It may be occurring at other RPMs (load) and not noticed? Goes away when warm?
Fuel Injector sticking Open? (which one).