High engine revs on start up

[CBX1000_imp]

Hi all

I've had my 2017 EX for 2 years now with just 2900 kms presently on the clock- I bought it used with 1800 kms. Over the last year or so I have had a scenario occur which is intermittent; when I turn the key to ignition on what should happen normally (BEFORE pressing the start button) is that both gauge needles should swing over clockwise & then re-settle to zero. Around 50% of the time this doesn't happen- only when I hit the start button do the needles swing round plus the engine revs crazily high momentarily & then settles to idle. This shouldn't be as the other 50% of the time the start up procedure is normal. Anyone else experience this & if so what was the problem?

Hoping for a resolution :-/

Cheers

Dave

 

[venturer434_imp]

Hello CBX1000,

1. Please re-check your battery post connections and ensure both terminals are tight.
2. Also check the health of your battery.

Hopefully the above will address the issues prior to the start - up .

As to high engine revs .. maybe there is something else going on..

 

[CBX1000_imp]

Hello CBX1000,

1. Please re-check your battery post connections and ensure both terminals are tight.
2. Also check the health of your battery.

Hopefully the above will address the issues prior to the start - up .

As to high engine revs .. maybe there is something else going on..

Thanks for your input- I'll do the checks as you've suggested

 

[CBX1000_imp]

Did a check today of the battery- terminals are indeed tight. Voltage is reading 12.8v without the engine running and increasing to just on 14v when idling. So I don't the battery is the issue here :huh:

 

[Cormanus]

Do you use your kill switch? If the kill switch is on and the engine has been disabled, the gauges do not sweep and the fuel pump doesn’t cycle when the ignition turns on. I’ve found that, if I start the engine while the fuel pump is cycling sand the gauges are sweeping, there’s a moment when the revs are abnormally high.

 

[pekingduck]

The IACV (intake air control valve) is a small stepper motor turning a threaded shaft that raises/lowers a piston within a chamber to control idle speed. When the key is turned on, it runs from one end of its range to the other to learn the limits. If the bike is started when it is still going through its cycle, it could/would cause the high idle.

 

[CBX1000_imp]

Do you use your kill switch? If the kill switch is on and the engine has been disabled, the gauges do not sweep and the fuel pump doesn’t cycle when the ignition turns on. I’ve found that, if I start the engine while the fuel pump is cycling sand the gauges are sweeping, there’s a moment when the revs are abnormally high.

I don't as a rule use the kill switch, however the gauges DO sweep with the kill switch either on or off when the ignition is turned on. With the kill switch on the fuel pump does not cycle.

The IACV (intake air control valve) is a small stepper motor turning a threaded shaft that raises/lowers a piston within a chamber to control idle speed. When the key is turned on, it runs from one end of its range to the other to learn the limits. If the bike is started when it is still going through its cycle, it could/would cause the high idle.

OK- as a test I'll delay hitting the start button once I've turned the ignition on & see what the result is

 

[Nachodaddy]

I had a problem on my 2013 standard in which the engine would start normally, but once warmed up, it would only idle at 2000rpm. Mine was solved by replacing the ECU.
Your problem seems somewhat different, so it may be an entirely different cause. One very costly fix that I tried unsuccessfully was to replace the intake air control valve (IACV). That cost about $700 to have done at a dealership and had no effect.
I discovered that by disconnecting the Throttle Position Sensor, the bike again idled at 1100 as it should and ran the way it was designed. RPM will be limited to 5,000 and the "Check Engine" light on the dash will light up. Disconnecting the TPS puts the bike in "Limp home" mode until you can fix it. You might try this and see if the bike runs the way it is supposed to. I don't know what it will tell you, but it may help you figure out what is going on. It is easy to disconnect and your bike will run fine and not be a safety hazard this way.
It is NOT a fix, but it might stop the high rpm and erratic running and help you find a fix.
Good luck.

 

[CBX1000_imp]

I had a problem on my 2013 standard in which the engine would start normally, but once warmed up, it would only idle at 2000rpm. Mine was solved by replacing the ECU.
Your problem seems somewhat different, so it may be an entirely different cause. One very costly fix that I tried unsuccessfully was to replace the intake air control valve (IACV). That cost about $700 to have done at a dealership and had no effect.
I discovered that by disconnecting the Throttle Position Sensor, the bike again idled at 1100 as it should and ran the way it was designed. RPM will be limited to 5,000 and the "Check Engine" light on the dash will light up. Disconnecting the TPS puts the bike in "Limp home" mode until you can fix it. You might try this and see if the bike runs the way it is supposed to. I don't know what it will tell you, but it may help you figure out what is going on. It is easy to disconnect and your bike will run fine and not be a safety hazard this way.
It is NOT a fix, but it might stop the high rpm and erratic running and help you find a fix.
Good luck.

Thanks for that- indeed something to think about. I would just clarify though that the high engine revs is just momentarily after hitting the start switch- the engine idles perfectly at all times. Also now that I've started waiting a little longer after turning the ignition on before hitting the start button the engine is not revving up as it did before...well not yet

 

[Nachodaddy]

Hey, that's good news! I'll keep my fingers crossed for you. I have the habit of turning on the key, twisting the throttle to full twice and then hitting the start button. That gives it a little bit of time, too.
:biker:

 

[Cormanus]

If you wait until the gauges finish sweeping and the fuel pump cycles the high revs shouldn’t occur.

 

[CBX1000_imp]

If you wait until the gauges finish sweeping and the fuel pump cycles the high revs shouldn’t occur.

Well that's just the problem; sometimes the gauges don't sweep at all until I press the start button & only then do they sweep fully together with the engine revving high for a moment.

I suspect that this is going to be a difficult issue to resolve...

 

[Cormanus]

May well be, CBX1000. Can you just time it to the fuel pump cycle? You hear that pretty clearly.

 

[CBX1000_imp]

May well be, CBX1000. Can you just time it to the fuel pump cycle? You hear that pretty clearly.

The fuel pump cycles every time I switch the ignition on (except when the kill switch is on, which is correct) so that appears to have no bearing on why the gauges randomly don't sweep & then produce the high revs on start up.

 

[Cormanus]

Sorry to belabour this, CBX1000, but, if you turn on the ignition and wait until the fuel pump cycles but the gauges don’t sweep, do you get the high revs? Or do you get the high revs only if you hit the start button before the fuel pump finishes cycling?

 

[CBX1000_imp]

Sorry to belabour this, CBX1000, but, if you turn on the ignition and wait until the fuel pump cycles but the gauges don’t sweep, do you get the high revs? Or do you get the high revs only if you hit the start button before the fuel pump finishes cycling?

The answer to the first part of your question is yes- I get the high revs without the gauges sweeping even after the fuel pump has cycled. As a rule I only hit the start button once the fuel pump has cycled- the cycle is actually pretty quick....essentially by the time you've turned the ignition on & then got your hand back to press the start button the pump cycle is already done

 

[Cormanus]

Right. Thanks. That one’s way beyond my pay grade, I’m afraid. It’s an odd thing to happen.

Maybe one our seriously knowledgeable members can help.

 

[Karidis]

I had saved this procedure from an old post.

Honda CB1100 High Idle Problem
* Warm up the bike to get normal operating temp and idling
* Ignition OFF and remove the key from the ignition switch
* Disconnect both battery cables from the battery terminals, the negative cable first
* Cover both battery terminals with a plastic bag/rag to prevent accidental cable to terminal reattachment
* Join both cables (- &+) together for about 10 minutes. If the battery cables are too short, jumper wire can be used
* Reconnect both cables back to the battery terminals, the positive cable first, then the negative.
* Ignition ON, wait until meters sweeping is completed 2-3 sec, start your bike and observe idling.....

 

[peterbaron]

The above procedure is known as ECU residual reset.
I use this method very often.
This may help permanently if no other hidden or intermittent problems occur or after replacing an electronic component.
Sure, it's good start and costs $0
In this particular case, when the engine is hot and at operating temperature, I would wiggle the TPS connector and watch the rpm.
Do one step at a time and start with wigling the TPS connector/3 wire

 

[Lord Popgun]

I have some ideas, but first I’d like to do some battery checks. Yeah, I know, you did some.

You said the resting voltage is 12.8v. Thats a good sign. Now with the meter on the battery, turn on the ignition. What is the voltage now?

Do you have a service manual? The manual says, and the wiring diagram shows, that the meter gets two 12v inputs. One is present all the time, and the other comes in when the ignition switch is turned on. The needles should sweep then. Could be an intermittent somewhere in the ignition 12v to the meter. It may be you have to open the meter and reseat/clean the connectors.

Why it works after started I don’t know yet. To me it indicates there isn’t enough voltage to operate the meter while under load but when the alternator comes up all is good. But then I wouldn’t expect the starter to have enough power to spin the engine but not drive the meters.

But one problem at a time. Check the voltage with ignition off, then on and tell us what the drop is.